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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2019	Nov. 12, 2019
Document and Entity Information [Abstract]
Entity Registrant Name	SpringWorks Therapeutics, Inc.
Entity Central Index Key	0001773427
Document Type	10-Q
Document Period End Date	Sep. 30, 2019
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Trading Symbol	SWTX
Entity Current Reporting Status	No
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Shell Company	false
Entity Ex Transition Period	false
Entity Common Stock, Shares Outstanding		43,006,077
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 343,825	$ 45,648
Prepaid expenses and other current assets	689	1,382
Total current assets	344,514	47,030
Property and equipment, net	820	317
Investment in VIE (MapKure)	999	0
Other Assets	2,062	1,043
Total assets	348,395	48,390
Current liabilities:
Accounts payable	2,157	774
Accrued expenses	7,682	2,568
Deferred rent	356	335
Total current liabilities	10,195	3,677
Long-term portion of deferred rent	881	1,152
Total liabilities	11,076	4,829
Commitments and contingencies
Stockholders' (deficit) equity:
Common stock, $0.0001 par value, 150,000,000 shares authorized, 43,233,387 shares issued and outstanding, at September 30, 2019; no shares authorized, issued or outstanding at December 31, 2018.	4	0
Common units, no par value; no units authorized, issued or outstanding at September 30, 2019; 195,638 units authorized, issued and outstanding at December 31, 2018.	0	0
Additional paid-in capital	394,127	1,069
Accumulated deficit	(56,812)	(22,452)
Total stockholders' (deficit) equity	337,319	(19,369)
Total liabilities, convertible preferred stock and stockholders' (deficit) equity	348,395	48,390
Series A Convertible Preferred Stock
Convertible preferred stock
Convertible preferred stocks	0	0
Series A Convertible Preferred Units
Convertible preferred stock
Convertible preferred stocks	0	62,930
Junior Series A Convertible Preferred Stock
Stockholders' (deficit) equity:
Junior Series A convertible preferred stocks	0	0
Junior Series A Convertible Preferred Units
Stockholders' (deficit) equity:
Junior Series A convertible preferred stocks	$ 0	$ 2,014

Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
Common stock, Par value	$ 0.0001	$ 0.0001
Common stock, Shares authorized	150,000,000	0
Common stock, Shares issued	43,233,387	0
Common stock, Shares outstanding	3,088,636	0
Common units, Par value	$ 0	$ 0
Common units, Shares authorized	0	195,638
Common units, Shares issued	0	195,638
Common units, Shares outstanding	0	195,638
Series A Convertible Preferred Stock
Temporary equity, Par value	$ 0.0001	$ 0.0001
Temporary equity, Shares authorized	0	0
Temporary equity, Shares issued	0	0
Temporary equity, Shares outstanding	0	0
Series A Convertible Preferred Units
Temporary equity units, Par value	$ 0	$ 0
Temporary equity units, Shares authorized	0	103,000,000
Temporary equity units, Shares issued	0	63,600,000
Temporary equity units, Shares outstanding	0	63,600,000
Junior Series A Convertible Preferred Stock
Preferred stock, Par value	$ 0	$ 0
Preferred stock, Shares authorized	0	0
Preferred stock, Shares issued	0	0
Preferred stock, Shares outstanding	0	0
Junior Series A Convertible Preferred Units
Preferred units, Par value	$ 0	$ 0
Preferred units, Shares authorized	0	6,437,500
Preferred units, Shares issued	0	6,437,500
Preferred units, Shares outstanding	0	6,437,500

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating expenses:
Research and development	$ 10,745	$ 3,406	$ 30,373	$ 6,192
General and administrative	4,584	1,824	11,495	5,852
Total operating expenses	15,329	5,230	41,868	12,044
Loss from operations	(15,329)	(5,230)	(41,868)	(12,044)
Other income:
Interest income, net	997	226	2,280	450
Total other Income	997	226	2,280	450
Net loss	(16,833)	(5,004)	(42,089)	(11,594)
Equity investment loss	(2,501)		(2,501)	0
Reconciliation of net loss to net loss attributable to common stockholders:
Net loss	(16,833)	(5,004)	(42,089)	(11,594)
Net gain attributable to extinguishment of Series A convertible preferred and Junior Series A convertible preferred shares	0	0	7,729	0
Net loss attributable to common stockholders - basic and diluted	$ (16,833)	$ (5,004)	$ (34,360)	$ (11,594)
Net loss per common unit, basic and diluted	$ 0.00	$ (11.55)	$ 0.00	$ (44.20)
Net loss per common share attributable to common stockholders, basic and diluted	$ (1.77)		$ (9.24)
Weighted average common units outstanding, basic and diluted	0	433,401	0	262,273
Weighted average common shares outstanding, basic and diluted	9,487,329		3,716,877

Consolidated Statement of Convertible Preferred Unit/Stock and Members'/Stockholders' Deficit - USD ($) $ in Thousands	Junior Series A Convertible Preferred Stock	Series B Convertible Preferred Stock	Series A and B Convertible Preferred Stock	Common stock options issued and outstanding	Additional Paid-in Capital	Accumulated Deficit	Total
Beginning balance at Dec. 31, 2017	$ 2,014		$ 12,554	$ 0	$ 0	$ (4,639)	$ (2,625)
Beginning balance (in shares) at Dec. 31, 2017	6,437,500		13,200,001	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of convertible preferred units, net			$ 50,376
Issuance of convertible preferred units, net (in shares)			50,399,999
Issuance of units (in shares)				195,638
Issuance of incentive units					609		609
Issuance of incentive units (in shares)				1,732,491
Net loss						(6,590)	(6,590)
Ending balance at Jun. 30, 2018	$ 2,014		$ 62,930		609	(11,229)	(8,606)
Ending balance (in shares) at Jun. 30, 2018	6,437,500		63,600,000	1,928,129
Beginning balance at Dec. 31, 2017	$ 2,014		$ 12,554	$ 0	0	(4,639)	(2,625)
Beginning balance (in shares) at Dec. 31, 2017	6,437,500		13,200,001	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss							(11,594)
Ending balance at Sep. 30, 2018	$ 2,014		$ 62,930		843	(16,233)	(13,376)
Ending balance (in shares) at Sep. 30, 2018	6,437,500		63,600,000	3,140,191
Beginning balance at Jun. 30, 2018	$ 2,014		$ 62,930		609	(11,229)	(8,606)
Beginning balance (in shares) at Jun. 30, 2018	6,437,500		63,600,000	1,928,129
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of incentive units					234		234
Issuance of incentive units (in shares)				1,212,062
Net loss						(5,004)	(5,004)
Ending balance at Sep. 30, 2018	$ 2,014		$ 62,930		843	(16,233)	(13,376)
Ending balance (in shares) at Sep. 30, 2018	6,437,500		63,600,000	3,140,191
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of incentive units					226	(6,219)	(5,993)
Issuance of incentive units (in shares)				42,725
Incentive units forfeited during the period (in shares)				(81,710)
Ending balance at Dec. 31, 2018	$ 2,014		$ 62,930		1,069	(22,452)	(19,369)
Ending balance (in shares) at Dec. 31, 2018	6,437,500		63,600,000	3,101,206
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of convertible preferred units, net		$ 124,590	$ 39,367
Issuance of convertible preferred units, net (in shares)		86,639,279	39,400,000
Convertible preferred extinguishment			$ (9,597)			9,597	9,597
Convertible preferred extinguishment	$ 1,868					(1,868)
Stock compensation expense, net of forfeiture					1,371		1,371
Stock compensation expense, net of forfeiture (in shares)				(12,570)
Net loss						(25,256)	(25,256)
Ending balance at Jun. 30, 2019	$ 3,882		$ 217,290		2,440	(39,979)	(33,657)
Ending balance (in shares) at Jun. 30, 2019	6,437,500		189,639,279	3,088,636
Beginning balance at Dec. 31, 2018	$ 2,014		$ 62,930		1,069	(22,452)	$ (19,369)
Beginning balance (in shares) at Dec. 31, 2018	6,437,500		63,600,000	3,101,206
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)							392
Net loss							$ (42,089)
Ending balance at Sep. 30, 2019				$ 4	394,127	(56,812)	337,319
Ending balance (in shares) at Sep. 30, 2019				43,233,387
Beginning balance at Jun. 30, 2019	$ 3,882		$ 217,290		2,440	(39,979)	(33,657)
Beginning balance (in shares) at Jun. 30, 2019	6,437,500		189,639,279	3,088,636
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of convertible preferred units, net				$ 1	169,729		169,730
Issuance of convertible preferred units, net (in shares)				10,350,000
Stock-based compensation					788		788
Conversion of convertible preferred stock into common stock	$ (3,882)		$ (217,290)	$ 3	221,169		217,290
Conversion of convertible preferred stock into common stock (in shares)	(6,437,500)		(189,639,279)	29,794,359
Exercise of stock options					1		1
Exercise of stock options (in shares)				392
Net loss						(16,833)	(16,833)
Ending balance at Sep. 30, 2019				$ 4	$ 394,127	$ (56,812)	$ 337,319
Ending balance (in shares) at Sep. 30, 2019				43,233,387

Consolidated Statement of Convertible Preferred Unit/Stock and Members'/Stockholders' Deficit (Parenthetical) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($)
Series B Convertible Preferred Stock
Legal Costs	$ 413,063

Consolidated Statements of Cash Flows - USD ($)	3 Months Ended	9 Months Ended		12 Months Ended
Consolidated Statements of Cash Flows - USD ($)	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Operating activities
Net loss		$ (42,089,000)	$ (11,594,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense		127,000	9,000	$ 9,325
Stock compensation expense		2,159,000	843,000
Equity investment loss	$ 2,501,000	2,501,000	0
Changes in operating assets and liabilities
Prepaid expenses and other current assets		693,000	(1,361,000)
Other assets		(1,019,000)	(542,000)
Accounts payable		1,383,000	(44,000)
Accrued expenses		5,114,000	1,478,000
Deferred rent		(250,000)	0
Net cash used in operating activities		(31,381,000)	(11,211,000)
Investing activities
Purchases of property and equipment		(630,000)	0
Investment in MapKure		(3,500,000)	0
Net cash used in investing activities		(4,130,000)	0
Financing activities
Proceeds from Issuance of Common Stock		169,730,000	0
Proceeds from issuance of Series A convertible preferred units, net of issuance costs		39,367,000	50,400,000
Proceeds from issuance of Series B convertible preferred units, net of issuance costs		124,590,000	0
Proceeds from stock option exercises		1,000	0
Net cash provided by financing activities		333,688,000	50,400,000
Net increase in cash and cash equivalents		298,177,000	39,189,000
Cash and cash equivalents, beginning of period		45,648,000	10,271,000	10,271,000
Cash and cash equivalents, end of period	$ 343,825,000	$ 343,825,000	$ 49,460,000	$ 45,648,000

Nature of Operations	9 Months Ended
Nature of Operations	Sep. 30, 2019
Nature of Operations
Nature of Operations	1. Nature of Operations SpringWorks Therapeutics, Inc. (The “Company”) was formed in Delaware on August 18, 2017 (“Inception”). Prior to March 29, 2019, the Company conducted its business through SpringWorks Therapeutics, LLC, a Delaware limited liability company. On March 29, 2019, it completed a series of transactions pursuant to which SpringWorks MergerSub LLC, a wholly owned subsidiary of SpringWorks Therapeutics, Inc., merged with SpringWorks Therapeutics, LLC, with SpringWorks Therapeutics, LLC surviving the merger as a wholly owned subsidiary of SpringWorks Therapeutics, Inc. (the “Reorganization”). The Company is a clinical-stage biopharmaceutical company focused on identifying, developing and commercializing therapies for underserved patient populations suffering from severe rare diseases and cancer. The Company has a pipeline of product candidates across various stages of development, currently focused on rare disease and oncology conditions. Two of the programs are late stage clinical product candidates: nirogacestat and mirdametinib. Initial Public Offering On September 12, 2019, the Company completed an initial public offering (IPO) of its common stock. In connections with its IPO, the Company issued and sold 10,350,000 shares of its common stock at a price to the public of $18.00 per share. The net proceeds from the IPO were approximately $169.7 million after deducting underwriting discounts and commissions of $13.0 million and offering expenses of approximately $3.5 million. At the closing of the IPO, 196,076,779 shares of outstanding convertible preferred stock were automatically converted into 29,794,359 shares of common stock at a conversion rate of one-for-6.5810. Following the IPO, there were no shares of preferred stock outstanding. Reverse Stock Split In August 2019, the Company’s Board of Directors and stockholders approved a one-for-6.5810 reverse stock split of the Company’s common stock. The reverse stock split became effective on August 30, 2019. Stockholders entitled to a fractional share as a result of the reverse stock split will receive a cash payment in lieu of the fractional shares at the initial public offering price. All common stock share and per share amounts in the consolidated financial statements and notes thereto have been retroactively adjusted, where applicable for all periods presented to give effect to the reverse stock split. The shares of common stock retained a par value of $0.0001 per share.

Risks and Liquidity	9 Months Ended
Risks and Liquidity	Sep. 30, 2019
Risks and Liquidity
Risks and Liquidity	2. Risks and Liquidity The Company has incurred losses and negative operating cash flows since Inception and had an accumulated deficit of $56.8 million and $22.5 million and working capital of $334.3 million and $43.4 million at September 30, 2019 and December 31, 2018, respectively. The Company is subject to those risks associated with any biopharmaceutical company that has substantial expenditures for development. There can be no assurance that the Company’s development projects will be successful, that products developed will obtain necessary regulatory approval, or that any approved product will be commercially viable. In addition, the Company operates in an environment of rapid technological change and is largely dependent on the services of its employees, advisors, consultants and vendors. The Company had cash and cash equivalents of $343.8 million and $45.6 million as of September 30, 2019 and December 31, 2018, respectively. In March 2019, the company received $39.4 million in net proceeds from the issuance of the third tranche of Series A convertible preferred units and raised an aggregate of $124.6 million of net proceeds from its Series B convertible preferred stock financing. In September 2019 , the Company completed its IPO whereby the Company sold an aggregate of 10,350,000 shares of its common stock for aggregate net proceeds of approximately $169.7 million. Based on the Company's cash and cash equivalents balance at September 30, 2019, management estimates that its cash and cash equivalents balance will enable it to meet operations expenses through at least twelve months after the date that the financial statements were available to be issued.

Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Sep. 30, 2019
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	3. Summary of Significant Accounting Policies Basis of Presentation These consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (U.S. GAAP). The consolidated financial statements include the accounts of the Company and all subsidiaries. All intercompany accounts and transactions have been eliminated. The Company does not have any components of other comprehensive income recorded within its consolidated financial statements, and, therefore, does not separately present a statement of comprehensive income in its consolidated financial statements. The Company's unaudited interim financial statements have been prepared by the Company in accordance with accounting principles generally accepted in the United States ("U.S. GAAP") for interim information and pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (the "SEC") for reporting on Form 10-Q. Accordingly, certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been or omitted pursuant to such rules and regulations. These unaudited interim financial statements should be read in conjunction with the audited financial statements and related notes included in the Company's final prospectus for its IPO, dated September 12, 2019, and filed with the SEC pursuant to Rule 424(b)(4) under the Securities Act of 1933. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts in the financial statements and accompanying notes. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, accrued expenses, the valuation of equity-based compensation and deferred tax asset valuation allowance. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates as there are changes in circumstances, facts and experience. Actual results may differ from those estimates or assumptions. The Company utilizes significant estimates and assumptions in determining the fair value of its common and incentive units, common stock, restricted stock and stock options. The Company has utilized various valuation methodologies in accordance with the framework of the American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately Held Company Equity Securities Issued as Compensation (the “Practice Aid”) to estimate the fair value of its common units and common stock. Each valuation methodology includes estimates and assumptions that require the Company’s judgment. These estimates and assumptions include a number of objective and subjective factors, including external market conditions, the prices at which the Company sold preferred units and convertible preferred stock, the rights and preferences of securities senior to the Company’s common and incentive units, and common stock and restricted stock at the time of, and the likelihood of, achieving a liquidity event, such as an initial public offering or sale. Significant changes to the key assumptions used in the valuations could result in different fair values at each valuation date. Segment Information Operating segments are defined as components of an entity about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment operating exclusively in the United States. Fair Value of Financial Instruments Management believes that the carrying amounts of the Company’s financial instruments, including accounts payable and accrued expenses, approximate fair value due to the short-term nature of those instruments. The Company follows the provisions of Financial Accounting Standards Board (“FASB”) ASC Topic 820, “Fair Value Measurements and Disclosures” (ASC 820), for financial assets and liabilities measured on a recurring basis. This pronouncement defines fair value, establishes a framework for measuring fair value under U.S. GAAP and requires expanded disclosures about fair value measurements. The guidance requires that fair value measurements be classified in one of the following three categories: Level 1 — Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets, or liabilities. Level 2 — Quoted prices for similar assets and liabilities in active markets, quoted prices in markets that are not active, or inputs which are observable, either directly or indirectly, for substantially the full term of the instrument. Level 3 — Prices or valuation techniques that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity). The Company considers all highly liquid instruments that have maturities of three months or less when acquired to be cash equivalents. The Company had cash and cash equivalents at September 30, 2019 of $343.8 million consisting of money market funds and are measured at fair value at the reporting date using quoted prices in active markets for identical assets (Level 1). The Company has no other financial assets or liabilities that are measured at fair value on a recurring basis. Cash and Cash Equivalents The Company considers all highly liquid instruments that have original maturities of three months or less when acquired to be cash equivalents. The Company had cash and cash equivalents at September 30, 2019 of $343.8 million. The Company maintains its bank accounts at one major financial institution. Concentration of Credit Risk Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company maintains each of its cash and cash equivalent balances with high quality, financial institutions and, accordingly, such funds are not exposed to significant credit risk. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. Research and Development Costs Research and Development Costs consist of expenses incurred in performing development activities, including salaries and benefits, equity-based compensation expenses, materials and supplies, preclinical expenses, clinical trial and related clinical manufacturing expenses, depreciation of equipment, contract services and other outside expenses. Costs for certain development activities, such as manufacturing and clinical trials, are recognized based on an evaluation of the progress to completion of specific tasks using either time-based measures or data such as information provided to the Company by its vendors on their actual costs incurred. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected in the consolidated financial statements as prepaid or accrued development expenses. Nonrefundable advance payments for goods or services to be received in the future for use in development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed. Equity-Based Compensation The Company accounts for employee equity-based compensation in accordance with Financial Accounting Standards Board Accounting Standards Codification Topic (“ASC”) 718, Compensation — Stock Compensation. ASC 718 requires all equity-based awards to employees and non-employee directors to be recognized as expense in the statement of operations based on the grant date fair value of the common and incentive unit, unit option, restricted stock and stock option awards. Equity-based awards vest over a four-year period. Generally, onboarding equity-based awards vest with the first 25% vesting following 12 months of employment or service and the remaining vesting in equal quarterly installments over the following 36 months. Certain restricted stock and stock options are subject to performance conditions and/or market conditions. Stock compensation expense is recognized using the straight-line method, based on the grant date fair value, over the requisite service period of the award, which is generally the vesting term. For awards subject to performance conditions, as well as awards containing both market and performance conditions, the Company recognizes equity award compensation expense using an accelerated recognition method over the remaining service period when management determines that achievement of the milestone is probable. Management evaluates when the achievement of a performance-based milestone is probable based on the expected satisfaction of the performance conditions as of the reporting date. The Company recognizes forfeitures at the time of the actual forfeiture event in accordance with the adoption of the guidance per Accounting Standard Update (“ASU”) No. 2016‑09. The grant-date fair value of performance-based awards with market conditions is estimated using a Monte Carlo simulation method that incorporates the probability of the performance conditions being met as of the grant date. For stock options issued, the Company estimates the grant date fair value and the resulting stock-based compensation expense using the Black-Scholes option-pricing model. The Black-Scholes option-pricing model requires the use of subjective assumptions which determine the fair value of stock-based awards, including the expected term and the price volatility of the underlying stock. The Company lacks company specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly-traded set of peer companies and expects to continue to do so until it has adequate historical data regarding the volatility of its own traded stock price. Net Loss per Unit and Share Basic net loss per unit and per share is computed by dividing net loss by the weighted average number of common units and shares outstanding for the period. Diluted net loss per unit and share excludes the potential impact of convertible preferred units, unvested incentive units, convertible preferred stock, unvested restricted stock and stock options because their effect would be anti-dilutive due to the Company’s net loss. Since the Company had a net loss in each of the periods presented, basic and diluted net loss per common unit and share are the same. Income Taxes Income taxes are accounted for using the asset-and-liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized as income in the period that includes the enactment date. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company recognizes deferred tax assets to the extent that we believe that these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies and results of recent operations. Valuation allowances are provided, if based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. If management determines that the Company would be able to realize its deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company records uncertain tax positions in accordance with ASC 740 on the basis of a two-step process in which (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more-likely-than-not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50% likely to be realized upon ultimate settlement with the related tax authority. The Company provides reserves for potential payments of tax to various tax authorities related to uncertain tax positions. These reserves are based on a determination of whether and how much of a tax benefit taken by the Company in its filings or positions is more likely than not to be realized following resolution of any potential contingencies related to the tax benefit. Potential interest related to the underpayment of income taxes will be classified as a component of income tax expense and any related penalties will be classified in income tax expenses in the statement of operations. SpringWorks Therapeutics, LLC elected to be treated under the partnership provisions of the Internal Revenue Service Code prior to the reorganization in March 29, 2019. However, its five wholly owned subsidiaries, SpringWorks Operating Company, SpringWorks Subsidiary 1, SpringWorks Subsidiary 2, SpringWorks Subsidiary 3, and SpringWorks Subsidiary 4, (“Combined Subsidiaries”) are taxable corporations. As of December 31, 2018, the Combined Subsidiaries had federal, state and city net operating loss carryforwards of $14.2 million, $0.6 million and $3.8 million, respectively, which are available to reduce future taxable income. Federal net operating loss carryforwards of $4.3 million were reported in 2017 and the state and city net operating loss carryforwards expire at various dates through 2038. Federal net operating loss carryforwards of $9.9 million reported in 2018 will be available to offset 80% of taxable income for an indefinite period of time, until fully utilized. The Combined Subsidiaries also have federal tax credits of $0.4 million, which may be used to offset future tax liabilities. These tax credit carryforwards will expire in 2038. Recently Issued Accounting Pronouncements (not yet adopted) In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”). ASU No. 2014-09 eliminated transaction- and industry-specific revenue recognition guidance under FASB ASC Subtopic 605-15, Revenue Recognition-Products and replaced it with a principle-based approach for determining revenue recognition. The new standard requires a company to recognize revenue upon transfer of goods or services to a customer at an amount that reflects the expected consideration to be received in exchange for those goods or services. ASU 2014-09 defines a five-step approach for recognizing revenue, which may require a company to use more judgment and make more estimates than under the current guidance. The standard is effective for annual periods beginning after December 15, 2018. The Company is currently evaluating the impact that ASU 2014-09 will have, if any, on its financial position, results of operations or cash flows. In February 2016, the FASB issued ASU 2016-02 “Leases (Topic 842).” This standard requires entities that lease assets to recognize on the balance sheet the assets and liabilities of the rights and obligations created by those leases. The standard is effective for annual periods beginning after December 15, 2019 and interim periods within annual periods beginning after December 15, 2020 for private companies. Early adoption is permitted. The Company will use the new transition option and is also utilizing the package of practical expedients that allows it to not reassess: (1) whether any expired or existing contracts are or contain leases, (2) lease classification for any expired or existing leases, and (3) initial direct costs for any expired or existing leases. The Company additionally expects to use the practical expedient that allows it to treat the lease and non-lease components of its leases as a single component. The Company has identified two leasing arrangements and is currently assessing the financial impact on the consolidated balance sheet. The Company qualifies as an emerging growth company (“EGC”) as defined under the Jumpstart Our Business Startups Act (the “JOBS Act”). Using exemptions provided under the JOBS Act provided to EGCs, the Company has elected to defer compliance with new or revised financial accounting standards until it is required to comply with such standards. In June 2018, the FASB issued ASU No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”). ASU 2018-07 expands the scope of Topic 718, Compensation – Stock Compensation, to include share-based payments issued to non-employees for goods or services. Consequently, non-employees and employees will be substantially aligned. ASU 2018-07 supersedes Subtopic 505-50, Equity – Equity-Based Payments to Non-Employees. The amendments are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted, but not earlier than the adoption of Topic 606, Revenue from contracts with customers. In August 2016, the FASB issued ASU 2016-15 “Statement of Cash Flows (Topic 230) — Classification of Certain Cash Receipts and Cash Payments.” This standard requires entities that must present a statement of cash flows under Topic 230 to classify certain cash receipts and cash payments using a standardized method. The standard is effective for annual periods beginning after December 15, 2018 and the interim periods within annual periods beginning after December 15, 2019. The guidance is required to be applied by the retrospective transition approach. Early adoption is permitted. The Company is currently assessing the impact of the adoption of this authoritative guidance on its consolidated financial statements. In August 2018, the FASB issued ASU No. 2018-15, Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”). The FASB issued ASU 2018-15 to align the requirements for capitalizing implementation costs incurred in a cloud-based hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. ASU 2018-15 is effective for annual and interim reporting periods beginning after December 15, 2019, and early adoption is permitted. The amendments under ASU 2018-15 may be applied either retrospectively or prospectively to all implementation costs incurred after adoption. The Company is evaluating the impact of ASU 2018-15 on its financial statements and the timing of adoption.

Property and Equipment

9 Months Ended

Sep. 30, 2019

Property and Equipment

Property and Equipment

4. Property and Equipment

Property and equipment, net consisted of the following:


	September 30,	December 31,
(in thousands)	2019	2018
Leasehold improvements	816	293
Computer equipment	121	27
Furniture	31	18
	968	338
Less accumulated depreciation	(148)	(21)
	820	317

Depreciation expense (unaudited) was $126,997 and $9,325 for the nine months ended September 30, 2019 and September 30, 2018, respectively.

Accrued Expenses

9 Months Ended

Sep. 30, 2019

Accrued Expenses

Accrued Expenses

5. Accrued Expenses

Accrued expenses consisted of the following:


	September 30,		December 31,
(in thousands)	2019		2018
Accrued professional fees	$	850	$	1,040
Accrued compensation and benefits		1,460		1,178
Accrued research and development		4,932		—
Accrued other		440		350
	$	7,682	$	2,568

Stockholders' Equity	9 Months Ended
Stockholders' Equity	Sep. 30, 2019
Stockholders' Equity
Stockholders' Equity	6. Stockholders’ Equity In August 2017, the Company authorized the sale and issuance of up to 103,000,000 units of Series A convertible preferred units at $1.00 per unit for a total of $103 million of proceeds. The Series A convertible preferred financing was structured to close in three tranches. The first tranche closed in August 2017, resulting in the issuance of 13,200,001 units of Series A convertible preferred units for gross cash proceeds of $13.2 million. In April 2018, the second tranche of 50,399,999 units of Series A convertible preferred were issued for $50.4 million in gross proceeds. In March 2019, the third tranche of 39,400,000 units of Series A convertible preferred units were issued for $39.4 million in gross proceeds. In August 2017 and in conjunction with the formation of the Company and the License Agreements (see Note 8), the Company authorized and issued 6,437,500 units of Junior Series A convertible preferred units in exchange for four license agreements for the development and commercialization of products based on the inventions of Pfizer’s researchers. No cash was received by the Company for these units. In March 2019, the Company authorized the sale and issuance of up to 86,639,279 shares of convertible preferred stock. The Series B convertible preferred financing was closed in a single tranche at the price of $1.4428 per share for net proceeds of $124.6 million; issuance costs totaled $0.4 million. The liquidation preference terms of each of the Series A convertible preferred stock and Junior Series A convertible preferred stock changed in connection with the issuance of Series B convertible preferred. Specifically, after receiving one times its original issue price, the Series A convertible preferred does not participate in the distribution with the Junior Series A convertible preferred prior to final distribution to all stockholders, and the Junior Series A convertible preferred does not participate with all other stockholders in the final distribution. The Company concluded that the changes in the Series A convertible preferred and Junior Series A convertible preferred liquidation preferences are a significant change in the economics of those instruments and therefore were accounted for as an extinguishment. Following the reverse split of the Company’s common stock in August 2019, every 6.5810 shares of Series A convertible preferred, Junior Series A convertible preferred and Series B convertible preferred became convertible into one common share at the option of the holder, subject to certain anti-dilution adjustments. The Series A convertible preferred, Junior Series A convertible preferred and Series B convertible preferred were mandatorily convertible in the event of an initial public offering, as defined. Upon completion of the Company's IPO in September 2019, all the outstanding preferred stock of the Company automatically converted into 29,794,359 shares of the Company's common stock. On September 12, 2019, the Company completed an IPO of its common stock. In connections with its IPO, the Company issued and sold 10,350,000 shares of its common stock. As of September 30, 2019, the Company has 150,000,000 shares authorized and 43,233,387 issued and outstanding common stock at $0.0001 par value.

Equity-Based Compensation

9 Months Ended

Sep. 30, 2019

Equity-Based Compensation

Equity-Based Compensation

7. Equity-Based Compensation

2018 Equity Plan

In January 2018, the Company adopted the 2018 Equity Incentive Plan (the “2018 Equity Plan”). There were 2,738,929 incentive units (“incentive units”) initially available for issuance under the 2018 Equity Plan. The 2018 Plan was increased by 269,716 units for an aggregate of 3,008,645 as of December 31, 2018.

The Company issued 3,290,929 and cancelled 385,361 incentive units during the twelve months ended December 31, 2018. There were 103,077 incentive units available for issuance at December 31, 2018. The total unrecognized compensation related to unvested incentive units granted was $2.5 million at December 31, 2018, which the Company expects to recognize over a period of approximately 3.5 years.

On March 19, 2019, the Company modified its operating agreement to allow for the award of unit options and granted a total of 148,415 unit options to certain employees, directors and consultants.

2019 Equity Plan

On March 29, 2019, the Company adopted the 2019 Stock Option and Incentive Plan (the “2019 Private Company Plan”) in connection with the Reorganization. The 2019 Private Company Plan originally had 5,292,355 shares available for issuance. In connection with the adoption of the 2019 Private Company Plan, all unit options granted on March 19, 2019 were exchanged for stock options, and all incentive units granted under the 2018 Equity Plan were exchanged for restricted stock. The restricted common stock was issued with the same vesting terms as the unvested incentive units held immediately prior to the Reorganization. On June 4, 2019, the total shares available for issuance under the 2019 Private Company Plan was increased to 5,382,828 shares. On July 29, 2019, the total shares available for issuance was increased to 6,700,197.

As of September 30, 2019 there were 2,892,998 shares of restricted stock and 3,023,714 shares of common stock issuable upon the exercise of outstanding stock option awards outstanding under the 2019 Equity Plan.

In connection with the IPO no modification was triggered for the 2019 Equity Plan and upon the effectiveness of the 2019 Public Company Plan (as defined below) no further grants will be made under the 2019 Private Company Plan. However, the shares of common stock underlying any awards that are forfeited, cancelled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of stock, expire or are otherwise terminated (other than by exercise) under the 2019 Private Company Plan will be added back to the shares of common stock available for issuance under the 2019 Public Company Plan.

2019 Equity Incentive Plan

In anticipation of the IPO, on August 30, 2019, the Company’s stockholders approved the 2019 Stock Option and Equity Incentive Plan (the “2019 Public Company Plan”), which became effective upon the effectiveness of the Company’s registration statement on September 12, 2019 in connection with the IPO.. The 2019 Public Company Plan provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock units, restricted stock awards, unrestricted stock awards and dividend equivalent rights to the Company’s officers, employees, directors and other key persons (including consultants). The number of shares initially reserved for issuance under the 2019 Public Company Plan is 3,537,225 shares, which shall be cumulatively increased on January 1, 2019 and each January 1 thereafter by 5% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or such lesser number of shares determined by the Company’s compensation committee.

The terms of stock options and restricted stock awards, including vesting requirements, are determined by the Board of Directors or its delegates, subject to the provisions of the 2019 Public Company Plan. Stock options and restricted stock awards granted by the Company to employees and directors generally vest over four years.

As of September 30, 2019, there were 3,352,840 shares available for future issuance under the 2019 Plan.

2019 Employee Stock Purchase Plan

On August 30, 2019, the Company’s stockholders approved the 2019 Employee Stock Purchase Plan (the “ESPP”), which became effective immediately preceding the effectiveness of the Company’s registration statement on September 12, 2019 in connection with the IPO. A total of 442,153 shares of common stock were reserved for issuance under the ESPP. In addition, the number of shares of common stock that may be issued under the ESPP will automatically increase on January 1, 2019, and each January 1 thereafter through January 1, 2028, by the lesser of (i) 663,229 shares of common stock, (ii) 1% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or (iii) such lesser number of shares determined by the administrator of the Company’s ESPP. No offering periods under the ESPP had been initiated as of September 30, 2019.

Stock Options

A summary of the changes in the Company’s stock options during the period nine months ended September 30, 2019:


			Weighted
			Average
		Weighted	Remaining
		Average	Contractual	Aggregate
		Exercise	Life	Intrinsic
	Shares	Price	(Years)	Value
Outstanding at December 31, 2018	—	—	—	—
Options granted	3,208,491	4.3	—	—
Option exercised	(392)	2.30	—	—
Options forfeited/cancelled	—	—	—	—
Outstanding at September 30, 2019	3,208,099	4.3	9.6	55,756,761
Options vested and exercisable at September 30, 2019	259,837	2.30	9.6	5,035,641

Aggregate intrinsic value is calculated by subtracting the exercise price of the option from the closing price of the Company's common stock on closing date, multiplied by the number of shares per each option.

Assumptions used in determining the fair value of the stock options granted in 2019 include risk-free interest rate 1.45% – 2.47%, expected dividend yield of 0.00%, expected Life in years of 5.75 - 6.25 and expected volatility of 68.1% - 71.0%.

Expected term?-?The expected term represents the period that the equity-based awards are expected to be outstanding. The expected term for our stock options was calculated based on the weighted average vesting term of the awards and the contract period, or simplified method.

Expected volatility?-?The Company lacks Company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until it has adequate historical data regarding the volatility of its own traded stock.

Risk-free interest rate?-?The risk-free interest rate is based on the U.S. Treasury yield in effect at the time of grant for zero-coupon U.S. Treasury notes with maturities approximately equal to the expected term of the awards.

Expected dividend?-?The Company has never paid dividends on its common units or stock and has no plans to pay dividends on its common stock. Therefore, the expected dividend yield is zero.

Fair Value of Common Stock - Prior to the IPO, the fair value of the shares of common stock underlying the stock-based awards were determined by the Company's Board of Directors with input from management. Since there was no public market for the common stock prior to September 12, 2019, the Company's Board of Directors had determined the fair value of the common stock at the time of grant of the stock-based award by considering a number of objective and subjective factors, including having valuations of the common stock performed by a third-party valuation specialist. The fair value of the common stock is now determined by the public market.

At September 30, 2019, the total unrecognized compensation related to unvested stock options was $9.0 million, which the Company expects to recognize over a period of approximately 4 years. For the nine months ended September 30, 2019 the stock option compensation expense was $0.9 million.

Restricted Stock

A summary of the changes in the Company's restricted stock during the year ended December 31, 2018 and September 30th, 2019.


		Weighted
		Average
	Number	Grant Date
	of Shares	Fair Value
Nonvested at December 31, 2018	2,503,744	1.25
Granted	—	—
Vested	(815,493)	1.15
Forfeited	(12,570)	1.45
Unvested and outstanding at September 30, 2019	1,675,681	1.22

The Company recorded total equity-based compensation expense related to restricted stock and stock options for the periods presented as follows (in thousands):


	Three Months Ended	Three Months Ended	Nine Months Ended	Nine Months Ended
	September 30, 2019	September 30, 2018	September 30, 2019	September 30, 2018
Research and development	194	56	505	102
General and administrative	594	179	1,654	741
Total equity compensation expenses	788	235	2,159	843

At September 30, 2019, the total unrecognized compensation related to unvested restricted stock was $1.2 million, which the Company expects to recognize over a period of approximately 3.0 years. For the nine months ended September 30, 2019 the restricted stock compensation expense was $1.3 million.

2019 CEO Performance Award

In June 2019, our CEO received an award of 176,411 stock options (the “2019 CEO Performance Award”) at an exercise price of $7.50 per share. The 2019 CEO Performance Award can vest over 48 monthly installments based on four years of service, a performance condition (a liquidity event, such as an IPO) and market conditions, assuming continued employment and service through each vesting date. During the vesting period of four years, the 2019 CEO Performance Award is not earned unless the market condition is achieved on each vesting date. If the market condition is not achieved on a vesting date, but is achieved on a future vesting date, the award is earned for the entire period since the last date that such market condition was achieved. All or a portion of the award can be earned following the initial four year service period if the market condition is next achieved after such four year service period and Mr. Islam remains in continuous service. The market condition and performance condition are satisfied when the Company’s common stock is listed on a U.S. national securities exchange and achieves a 60‑trading day average closing price of at least $28.49 per share (as adjusted for stock splits, recapitalizations, and similar events).

As a result of the IPO, the performance conditions have been met; however the market condition is not yet satisfied as of September 30, 2019.

The Company recorded $0.2 million stock compensation expense related to this award as of September 30, 2019.

At September 30, 2019, the total unrecognized compensation related to the unvested CEO Performance Award was $1.2 million, which the Company expects to recognize over a period of approximately 3.67 years.

License and Collaboration Agreements	9 Months Ended
License and Collaboration Agreements	Sep. 30, 2019
License and Collaboration Agreements
License and Collaboration Agreements	8. License and Collaboration Agreements Pfizer Inc. In August and October 2017, the Subsidiaries entered into four license agreements with Pfizer for rights to certain technologies (the “License Agreements”). Under the License Agreements, the Company obtained from Pfizer the right to use research, develop, manufacture and commercialize certain products, including nirogacestat and mirdametinib. In connection with the License Agreements, the Company issued 6,437,500 units of Junior Series A convertible preferred units to Pfizer (see Note 6). No cash was received by the Company for these units. The Company is required to pay Pfizer milestones payments of up to an aggregate of $232.5 million for nirogacestat and up to an aggregate of $229.8 million for mirdametinib, each upon achievement of certain commercial milestone events. Royalties are also payable under each License Agreement based on a specified percentage of net sales ranging from mid-single digit percentages to the low 20s, Royalty payments under each License Agreement continue until the expiration of the last to expire licensed patent applicable to such product, but not less than ten years after the first commercial sale on a country-by-country basis. BeiGene, Ltd. (“BeiGene”) In August 2018, the Company entered into a clinical collaboration agreement with BeiGene to conduct a clinical study of the combination of mirdametinib and a BeiGene compound designated as lifirafenib. In accordance with the terms of the agreement, the Company and BeiGene share equally the costs associated with the clinical study. BeiGene is required to supply the BeiGene compound and the Company is required to supply mirdametinib to conduct the clinical study. The collaboration is guided by a joint steering committee. Specified areas of development require unanimous agreement among all members of the joint steering committee. The Company recorded $0.8 million and $0.4 million for the nine months ended September 30, 2019 and December 31, 2018, respectively. GSK clinical collaboration agreement (“GSK”) In June 2019, the Company entered into a clinical collaboration agreement with GlaxoSmithKline (“GSK”) (the “GSK Collaboration Agreement”), to evaluate the safety, tolerability and preliminary efficacy of nirogacestat and belantamab mafodotin. Under the terms of the GSK Collaboration Agreement, GSK will sponsor and conduct the adaptive Phase 1b study of nirogacestat, in combination with GSK’s BCMA antibody-drug conjugate, belantamab mafodotin, in patients with relapsed or refractory multiple myeloma. GSK will assume all development costs associated with the study. The Company agreed to manufacture and supply the Company compound for purposes of the study. Pursuant to the GSK Collaboration Agreement, GSK is responsible for administering the clinical trial and is responsible for all costs associated with the direct conduct of the clinical trial, other than the manufacture and supply of nirogacestat and certain expenses related to intellectual property rights. The collaboration is managed by a joint development committee of equal representation by the Company and GSK. Following completion of the clinical trial, within a specified period of time, either party may propose new agreements for the purpose of performing one or more additional clinical trials of the combination therapy for the treatment of relapsed and refractory multiple myeloma. If a party proposes to conduct an additional clinical trial, the parties will negotiate in good faith, without obligation, the details of a definitive agreement to provide for the expansion of the clinical collaboration. If the parties do not reach an agreement, and only one party wishes to proceed with an additional clinical trial, it may do so if the other party does not object to the protocol based on safety concerns. The Company has not incurred any expense under the GSK Collaboration Agreement as of September 30, 2019.

Commitments and Contingencies

9 Months Ended

Sep. 30, 2019

Commitments and Contingencies

Commitments and Contingencies

9. Commitments and Contingencies

Leases

In August 2018, the Company entered into a five-year operating lease in Durham, NC (the location of the Company’s clinical development operations), with two five-year renewal options. Rental payments under the renewal period will be at current market rates for the premises. The Company established a security deposit of $40,467 presented in other assets.

In October 2018, the Company entered into a lease for its corporate headquarters in Stamford, CT. The lease expires in November 2022. The Company received $1.5 million from the previous tenant in connection with the assumption of the lease. The Company recognizes rent expense for the office it currently occupies and records a deferred rent obligation representing the cumulative difference between actual rent payments, incentive received and rent expense recognized ratably over the lease period. The Company established a security deposit of $0.5 million in the form of a letter-of-credit, recorded in other noncurrent assets.

The Company’s future minimum lease obligations as of September 30, 2019 are:


	Premises Operating
(in thousands)	Leases
Remainder of 2019	$	331
2020		1,344
2021		1,372
2022		1,297
2023		135
Total Obligations	$	4,479

The Company recorded rent expense of $0.7 million and $0.2 million for the nine months ended September 30, 2019, and September 30, 2018, respectively.

Contingencies

From time to time, the Company may be involved in disputes or regulatory inquiries that arise in the ordinary course of business. When the Company determines that a loss is both probable and reasonably estimable, a liability is recorded and disclosed if the amount is material to the financial statements taken as a whole. When a material loss contingency is only reasonably possible, the Company does not record a liability, but instead discloses the nature and the amount of the claim, and an estimate of the loss or range of loss, if such an estimate can reasonably be made.

As of September 30, 2019, there was no litigation or contingency with at least a reasonable possibility of a material loss.

Net Loss per Share and Unit

9 Months Ended

Sep. 30, 2019

Net Loss per Share and Unit

Net Loss per Share and Unit

10. Net Loss per Share and Unit

Basic and diluted net loss per unit is calculated as follows:


	Three Months Ended		Nine Months Ended
(in thousands, except unit and per unit data and share and per share data)	September 30, 2019	September 30, 2018	September 30, 2019	September 30, 2018
Net Loss attributable to common stockholder - basic and diluted	(16,833)	(5,004)	(34,360)	(11,594)
Weighted average common units outstanding, basic and diluted	—	433,401	—	262,273
Weighted average common shares outstanding, basic and diluted	9,487,329	—	3,716,877	—
Net Loss per unit, basic and diluted	—	(11.55)	—	(44.20)
Net Loss per share, basic and diluted	(1.77)	—	(9.24)	—

The table below provides potential common shares not included in the calculation of the diluted net loss per share because to do so would be anti-dilutive:


	as of September 30,
	2019	2018
Common stock options issued and outstanding	3,208,099	—
Restricted stock subject to future vesting	1,675,681	2,637,674
	4,883,780	2,637,674

Investment and Variable Interest Entity	9 Months Ended
Investment and Variable Interest Entity	Sep. 30, 2019
Investment and Variable Interest Entity
Investment and Variable Interest Entity	11. Investment and Variable Interest Entity MapKure June 2019, the Company announced the formation of MapKure, an entity jointly owned by the Company and BeiGene. BeiGene licensed to MapKure exclusive rights to BGB‑3245, an oral, small molecule selective inhibitor of specific BRAF driver mutations and genetic fusions. MapKure intends to advance BGB‑3245 into clinical development for solid tumor patients harboring BRAF driver mutations and genetic fusions that were observed to be sensitive to the compound in preclinical studies. In addition to the Company’s equity ownership in MapKure, the Company has appointed a member to each of MapKure’s joint steering committee and board of directors. The Company will also contribute to clinical development and other operational activities for BGB‑3245 through a service agreement with MapKure. The Company purchased 3,500,000 Series A preferred units of MapKure, or a 25% ownership interest, of the outstanding unit for $3.5 million, and BeiGene received 10,000,000 Series A preferred units as payment for its contributed intellectual property, or a 71.4% ownership interest. Two individuals each purchased 250,000 Series A preferred units, or 1.8% ownership interest each. Upon the first anniversary of the initial closing (the “Second Closing”), MapKure is obligated to sell another 4,000,000 Series A preferred units to the same two individuals and the Company. At the Second Closing, the Company is obligated to purchase 3,500,000 Series A preferred units, which will increase the Company’s ownership to 38.9%. The Company determined that MapKure is a variable interest entity, but the Company is not the primary beneficiary. The Company does not have the power to direct the activities that most significantly impact the economic performance of MapKure. Accordingly, the Company does not consolidate the financial statements of this entity and accounts for this investment using equity method accounting. In accordance with ASC 323-10-35-6, the Company records MapKure’s earnings or losses based on a one quarter lag. The Company recognized $2.5 million equity loss for the nine months ended September 30, 2019. The Company’s ownership interest in MapKure is included in “Equity method investments” in the Consolidated Balance Sheet as of September 30, 2019. The balance of the Company’s investment was $1.0 million at September 30, 2019, representing the maximum exposure to loss as a result of the Company’s involvement with MapKure.

Related Party Transactions	9 Months Ended
Related Party Transactions	Sep. 30, 2019
Related Party Transactions
Related Party Transactions	12. Related Party Transactions Prior to the Company becoming public, the company entered into agreements with two of its board members to provide consulting and Board of Director ("BOD") services to the Company. For the year ended December 31, 2018, the Company recorded consulting and BOD expenses totaling $287,079. The Company recorded consulting and BOD expenses totaling $216,417 to the IPO date for the nine months ended September 30, 2019 and $193,133 for the nine months ended September 30, 2018.

Subsequent Events	9 Months Ended
Subsequent Events	Sep. 30, 2019
Subsequent Events
Subsequent Events	13. Subsequent Events The Company has evaluated subsequent events through November 12, 2019, the date on which the financial statements were available to be issued.

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2019
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation These consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (U.S. GAAP). The consolidated financial statements include the accounts of the Company and all subsidiaries. All intercompany accounts and transactions have been eliminated.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts in the financial statements and accompanying notes. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, accrued expenses, the valuation of equity-based compensation and deferred tax asset valuation allowance. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates as there are changes in circumstances, facts and experience. Actual results may differ from those estimates or assumptions. The Company utilizes significant estimates and assumptions in determining the fair value of its common and incentive units, common stock, restricted stock and stock options. The Company has utilized various valuation methodologies in accordance with the framework of the American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately Held Company Equity Securities Issued as Compensation (the “Practice Aid”) to estimate the fair value of its common units and common stock. Each valuation methodology includes estimates and assumptions that require the Company’s judgment. These estimates and assumptions include a number of objective and subjective factors, including external market conditions, the prices at which the Company sold preferred units and convertible preferred stock, the rights and preferences of securities senior to the Company’s common and incentive units, and common stock and restricted stock at the time of, and the likelihood of, achieving a liquidity event, such as an initial public offering or sale. Significant changes to the key assumptions used in the valuations could result in different fair values at each valuation date.
Segment Information	Segment Information Operating segments are defined as components of an entity about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment operating exclusively in the United States.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Management believes that the carrying amounts of the Company’s financial instruments, including accounts payable and accrued expenses, approximate fair value due to the short-term nature of those instruments. The Company follows the provisions of Financial Accounting Standards Board (“FASB”) ASC Topic 820, “Fair Value Measurements and Disclosures” (ASC 820), for financial assets and liabilities measured on a recurring basis. This pronouncement defines fair value, establishes a framework for measuring fair value under U.S. GAAP and requires expanded disclosures about fair value measurements. The guidance requires that fair value measurements be classified in one of the following three categories: Level 1 — Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets, or liabilities. Level 2 — Quoted prices for similar assets and liabilities in active markets, quoted prices in markets that are not active, or inputs which are observable, either directly or indirectly, for substantially the full term of the instrument. Level 3 — Prices or valuation techniques that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity). The Company considers all highly liquid instruments that have maturities of three months or less when acquired to be cash equivalents. The Company had cash and cash equivalents at September 30, 2019 of $343.8 million consisting of money market funds and are measured at fair value at the reporting date using quoted prices in active markets for identical assets (Level 1). The Company has no other financial assets or liabilities that are measured at fair value on a recurring basis.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid instruments that have original maturities of three months or less when acquired to be cash equivalents. The Company had cash and cash equivalents at September 30, 2019 of $343.8 million. The Company maintains its bank accounts at one major financial institution.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company maintains each of its cash and cash equivalent balances with high quality, financial institutions and, accordingly, such funds are not exposed to significant credit risk. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.
Research and Development	Research and Development Costs Research and Development Costs consist of expenses incurred in performing development activities, including salaries and benefits, equity-based compensation expenses, materials and supplies, preclinical expenses, clinical trial and related clinical manufacturing expenses, depreciation of equipment, contract services and other outside expenses. Costs for certain development activities, such as manufacturing and clinical trials, are recognized based on an evaluation of the progress to completion of specific tasks using either time-based measures or data such as information provided to the Company by its vendors on their actual costs incurred. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected in the consolidated financial statements as prepaid or accrued development expenses. Nonrefundable advance payments for goods or services to be received in the future for use in development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed.
Equity-Based Compensation	Equity-Based Compensation The Company accounts for employee equity-based compensation in accordance with Financial Accounting Standards Board Accounting Standards Codification Topic (“ASC”) 718, Compensation — Stock Compensation. ASC 718 requires all equity-based awards to employees and non-employee directors to be recognized as expense in the statement of operations based on the grant date fair value of the common and incentive unit, unit option, restricted stock and stock option awards. Equity-based awards vest over a four-year period. Generally, onboarding equity-based awards vest with the first 25% vesting following 12 months of employment or service and the remaining vesting in equal quarterly installments over the following 36 months. Certain restricted stock and stock options are subject to performance conditions and/or market conditions. Stock compensation expense is recognized using the straight-line method, based on the grant date fair value, over the requisite service period of the award, which is generally the vesting term. For awards subject to performance conditions, as well as awards containing both market and performance conditions, the Company recognizes equity award compensation expense using an accelerated recognition method over the remaining service period when management determines that achievement of the milestone is probable. Management evaluates when the achievement of a performance-based milestone is probable based on the expected satisfaction of the performance conditions as of the reporting date. The Company recognizes forfeitures at the time of the actual forfeiture event in accordance with the adoption of the guidance per Accounting Standard Update (“ASU”) No. 2016‑09. The grant-date fair value of performance-based awards with market conditions is estimated using a Monte Carlo simulation method that incorporates the probability of the performance conditions being met as of the grant date. For stock options issued, the Company estimates the grant date fair value and the resulting stock-based compensation expense using the Black-Scholes option-pricing model. The Black-Scholes option-pricing model requires the use of subjective assumptions which determine the fair value of stock-based awards, including the expected term and the price volatility of the underlying stock. The Company lacks company specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly-traded set of peer companies and expects to continue to do so until it has adequate historical data regarding the volatility of its own traded stock price.
Net Loss per Unit and Share	Net Loss per Unit and Share Basic net loss per unit and per share is computed by dividing net loss by the weighted average number of common units and shares outstanding for the period. Diluted net loss per unit and share excludes the potential impact of convertible preferred units, unvested incentive units, convertible preferred stock, unvested restricted stock and stock options because their effect would be anti-dilutive due to the Company’s net loss. Since the Company had a net loss in each of the periods presented, basic and diluted net loss per common unit and share are the same.
Income Taxes	Income Taxes Income taxes are accounted for using the asset-and-liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized as income in the period that includes the enactment date. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company recognizes deferred tax assets to the extent that we believe that these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies and results of recent operations. Valuation allowances are provided, if based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. If management determines that the Company would be able to realize its deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company records uncertain tax positions in accordance with ASC 740 on the basis of a two-step process in which (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more-likely-than-not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50% likely to be realized upon ultimate settlement with the related tax authority. The Company provides reserves for potential payments of tax to various tax authorities related to uncertain tax positions. These reserves are based on a determination of whether and how much of a tax benefit taken by the Company in its filings or positions is more likely than not to be realized following resolution of any potential contingencies related to the tax benefit. Potential interest related to the underpayment of income taxes will be classified as a component of income tax expense and any related penalties will be classified in income tax expenses in the statement of operations. SpringWorks Therapeutics, LLC elected to be treated under the partnership provisions of the Internal Revenue Service Code prior to the reorganization in March 29, 2019. However, its five wholly owned subsidiaries, SpringWorks Operating Company, SpringWorks Subsidiary 1, SpringWorks Subsidiary 2, SpringWorks Subsidiary 3, and SpringWorks Subsidiary 4, (“Combined Subsidiaries”) are taxable corporations. As of December 31, 2018, the Combined Subsidiaries had federal, state and city net operating loss carryforwards of $14.2 million, $0.6 million and $3.8 million, respectively, which are available to reduce future taxable income. Federal net operating loss carryforwards of $4.3 million were reported in 2017 and the state and city net operating loss carryforwards expire at various dates through 2038. Federal net operating loss carryforwards of $9.9 million reported in 2018 will be available to offset 80% of taxable income for an indefinite period of time, until fully utilized. The Combined Subsidiaries also have federal tax credits of $0.4 million, which may be used to offset future tax liabilities. These tax credit carryforwards will expire in 2038.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements (not yet adopted) In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”). ASU No. 2014-09 eliminated transaction- and industry-specific revenue recognition guidance under FASB ASC Subtopic 605-15, Revenue Recognition-Products and replaced it with a principle-based approach for determining revenue recognition. The new standard requires a company to recognize revenue upon transfer of goods or services to a customer at an amount that reflects the expected consideration to be received in exchange for those goods or services. ASU 2014-09 defines a five-step approach for recognizing revenue, which may require a company to use more judgment and make more estimates than under the current guidance. The standard is effective for annual periods beginning after December 15, 2018. The Company is currently evaluating the impact that ASU 2014-09 will have, if any, on its financial position, results of operations or cash flows. In February 2016, the FASB issued ASU 2016-02 “Leases (Topic 842).” This standard requires entities that lease assets to recognize on the balance sheet the assets and liabilities of the rights and obligations created by those leases. The standard is effective for annual periods beginning after December 15, 2019 and interim periods within annual periods beginning after December 15, 2020 for private companies. Early adoption is permitted. The Company will use the new transition option and is also utilizing the package of practical expedients that allows it to not reassess: (1) whether any expired or existing contracts are or contain leases, (2) lease classification for any expired or existing leases, and (3) initial direct costs for any expired or existing leases. The Company additionally expects to use the practical expedient that allows it to treat the lease and non-lease components of its leases as a single component. The Company has identified two leasing arrangements and is currently assessing the financial impact on the consolidated balance sheet. The Company qualifies as an emerging growth company (“EGC”) as defined under the Jumpstart Our Business Startups Act (the “JOBS Act”). Using exemptions provided under the JOBS Act provided to EGCs, the Company has elected to defer compliance with new or revised financial accounting standards until it is required to comply with such standards. In June 2018, the FASB issued ASU No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”). ASU 2018-07 expands the scope of Topic 718, Compensation – Stock Compensation, to include share-based payments issued to non-employees for goods or services. Consequently, non-employees and employees will be substantially aligned. ASU 2018-07 supersedes Subtopic 505-50, Equity – Equity-Based Payments to Non-Employees. The amendments are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted, but not earlier than the adoption of Topic 606, Revenue from contracts with customers. In August 2016, the FASB issued ASU 2016-15 “Statement of Cash Flows (Topic 230) — Classification of Certain Cash Receipts and Cash Payments.” This standard requires entities that must present a statement of cash flows under Topic 230 to classify certain cash receipts and cash payments using a standardized method. The standard is effective for annual periods beginning after December 15, 2018 and the interim periods within annual periods beginning after December 15, 2019. The guidance is required to be applied by the retrospective transition approach. Early adoption is permitted. The Company is currently assessing the impact of the adoption of this authoritative guidance on its consolidated financial statements. In August 2018, the FASB issued ASU No. 2018-15, Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”). The FASB issued ASU 2018-15 to align the requirements for capitalizing implementation costs incurred in a cloud-based hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. ASU 2018-15 is effective for annual and interim reporting periods beginning after December 15, 2019, and early adoption is permitted. The amendments under ASU 2018-15 may be applied either retrospectively or prospectively to all implementation costs incurred after adoption. The Company is evaluating the impact of ASU 2018-15 on its financial statements and the timing of adoption.

Property and Equipment (Tables)

9 Months Ended

Sep. 30, 2019

Property and Equipment

Property and equipment, net


	September 30,	December 31,
(in thousands)	2019	2018
Leasehold improvements	816	293
Computer equipment	121	27
Furniture	31	18
	968	338
Less accumulated depreciation	(148)	(21)
	820	317

Accrued Expenses (Tables)

9 Months Ended

Sep. 30, 2019

Accrued Expenses

Schedule of accrued expenses

Accrued expenses consisted of the following:


	September 30,		December 31,
(in thousands)	2019		2018
Accrued professional fees	$	850	$	1,040
Accrued compensation and benefits		1,460		1,178
Accrued research and development		4,932		—
Accrued other		440		350
	$	7,682	$	2,568

Equity-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2019

Equity-Based Compensation

Summary of changes in the Company's stock options


			Weighted
			Average
		Weighted	Remaining
		Average	Contractual	Aggregate
		Exercise	Life	Intrinsic
	Shares	Price	(Years)	Value
Outstanding at December 31, 2018	—	—	—	—
Options granted	3,208,491	4.3	—	—
Option exercised	(392)	2.30	—	—
Options forfeited/cancelled	—	—	—	—
Outstanding at September 30, 2019	3,208,099	4.3	9.6	55,756,761
Options vested and exercisable at September 30, 2019	259,837	2.30	9.6	5,035,641

Summary of changes in the Company's restricted stock


		Weighted
		Average
	Number	Grant Date
	of Shares	Fair Value
Nonvested at December 31, 2018	2,503,744	1.25
Granted	—	—
Vested	(815,493)	1.15
Forfeited	(12,570)	1.45
Unvested and outstanding at September 30, 2019	1,675,681	1.22

Summary of equity-based compensation expense related to restricted stock and stock options


	Three Months Ended	Three Months Ended	Nine Months Ended	Nine Months Ended
	September 30, 2019	September 30, 2018	September 30, 2019	September 30, 2018
Research and development	194	56	505	102
General and administrative	594	179	1,654	741
Total equity compensation expenses	788	235	2,159	843

Commitments and Contingencies (Tables)

9 Months Ended

Sep. 30, 2019

Commitments and Contingencies

Schedule of Future minimum lease obligations

The Company’s future minimum lease obligations as of September 30, 2019 are:


	Premises Operating
(in thousands)	Leases
Remainder of 2019	$	331
2020		1,344
2021		1,372
2022		1,297
2023		135
Total Obligations	$	4,479

Net Loss per Share and Unit (Tables)

9 Months Ended

Sep. 30, 2019

Net Loss per Share and Unit

Schedule of Basic and diluted net loss per share


	Three Months Ended		Nine Months Ended
(in thousands, except unit and per unit data and share and per share data)	September 30, 2019	September 30, 2018	September 30, 2019	September 30, 2018
Net Loss attributable to common stockholder - basic and diluted	(16,833)	(5,004)	(34,360)	(11,594)
Weighted average common units outstanding, basic and diluted	—	433,401	—	262,273
Weighted average common shares outstanding, basic and diluted	9,487,329	—	3,716,877	—
Net Loss per unit, basic and diluted	—	(11.55)	—	(44.20)
Net Loss per share, basic and diluted	(1.77)	—	(9.24)	—

Schedule of potential common units not included in the calculation of the diluted net loss per unit and share


	as of September 30,
	2019	2018
Common stock options issued and outstanding	3,208,099	—
Restricted stock subject to future vesting	1,675,681	2,637,674
	4,883,780	2,637,674

Nature of Operations (Details) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended	9 Months Ended
	Sep. 12, 2019 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) $ / shares shares	Aug. 31, 2019	Sep. 30, 2019 USD ($) $ / shares	Sep. 30, 2019 USD ($) $ / shares	Sep. 30, 2018 USD ($)	Dec. 31, 2018 $ / shares
Subsidiary, Sale of Stock [Line Items]
Proceeds from Issuance of Common Stock					$ 169,730	$ 0
Payments of Stock Issuance Costs				$ 16,570
Reverse stock split			0.0001
Common stock par value \| $ / shares		$ 0.0001		$ 0.0001	$ 0.0001		$ 0.0001
IPO [Member]
Subsidiary, Sale of Stock [Line Items]
Stock Issued During Period, Shares, New Issues \| shares	10,350,000	10,350,000
Share Price \| $ / shares	$ 18.00
Net proceeds from the IPO	$ 169,700	$ 169,700
Underwriting discounts and commissions	13,000
Payments of Stock Issuance Costs	$ 3,500
Number of shares converted \| shares	196,076,779
Number of shares issued upon conversion \| shares	29,794,359
Conversion rate	0.15195%
Preferred stock outstanding \| shares	0

Risks and Liquidity (Details) - USD ($) $ in Thousands		1 Months Ended		9 Months Ended
Risks and Liquidity (Details) - USD ($) $ in Thousands	Sep. 12, 2019	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Risks and Liquidity
Accumulated deficit		$ (56,812)		$ (56,812)		$ (22,452)
Working Capital		334,300		334,300		43,400
Cash and cash equivalents		$ 343,825		343,825		$ 45,648
Net increase in cash and cash equivalents				298,177	$ 39,189
Proceeds from issuance of Series A convertible preferred units, net of issuance costs			$ 39,400	39,367	50,400
Proceeds from issuance of Series B convertible preferred units, net of issuance costs			$ 124,600	$ 124,590	$ 0
IPO [Member]
Risks and Liquidity
Units issued to certain employees	10,350,000	10,350,000
Net proceeds from the IPO	$ 169,700	$ 169,700

Summary of Significant Accounting Policies - Unaudited Pro Forma Information, Segment Information & Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Cash and Cash Equivalents
Cash and Cash Equivalents, at Carrying Value	$ 343,825	$ 45,648

Summary of Significant Accounting Policies - Equity-based compensation expense (Details)	1 Months Ended	9 Months Ended
	Jun. 30, 2019	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years	4 years
Vesting percentage		25.00%
First tranche, August 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		12 months
Second tranche, April 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		36 months

Summary of Significant Accounting Policies - Income Taxes (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Federal net operating loss carryforwards		$ 14.2	$ 4.3
State net operating loss carryforwards		0.6
City net operating loss carryforwards		$ 3.8
Federal net operating loss carryforwards for an indefinite period of time	$ 9.9
Federal net operating loss carryforwards available to offset percentage of taxable income	80.00%
Federal tax credits	$ 0.4

Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Property and Equipment
Property, Plant and Equipment, Gross	$ 968	$ 338
Less accumulated depreciation	(148)	(21)
Property, Plant and Equipment, Net	820	317
Leasehold improvements
Property and Equipment
Property, Plant and Equipment, Gross	816	293
Computer equipment
Property and Equipment
Property, Plant and Equipment, Gross	121	27
Furniture
Property and Equipment
Property, Plant and Equipment, Gross	$ 31	$ 18

Property and Equipment - Additional Information (Details) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Property and Equipment
Depreciation expense	$ 127,000	$ 9,000	$ 9,325

Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accrued Expenses
Accrued professional fees	$ 850	$ 1,040
Accrued compensation and benefits	1,460	1,178
Accrued research and development	4,932
Accrued other	440	350
Accrued expenses	$ 7,682	$ 2,568

Stockholders' Equity (Details) $ / shares in Units, $ in Thousands	1 Months Ended				3 Months Ended	9 Months Ended
	Aug. 31, 2019	Mar. 31, 2019 USD ($) $ / shares shares	Apr. 30, 2018 USD ($) shares	Aug. 31, 2017 USD ($) item $ / shares shares	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2019 $ / shares shares	Dec. 31, 2018 $ / shares shares
Preferred Units, Preferred Partners' Capital Account [Abstract]
Issuance costs \| $					$ 16,570
Stockholders' Equity Note, Stock Split, Conversion Ratio	0.0001
Common Stock, Shares, Outstanding					3,088,636	3,088,636	0
Common Stock, Shares, Issued					43,233,387	43,233,387	0
Common Stock, Shares Authorized					150,000,000	150,000,000	0
Common Stock, Par or Stated Value Per Share \| $ / shares					$ 0.0001	$ 0.0001	$ 0.0001
Series A Convertible Preferred Units
Preferred Units, Preferred Partners' Capital Account [Abstract]
Number of preferred units authorized				103,000,000
Price per unit \| $ / shares				$ 1.00
Gross cash proceeds from issuance \| $				$ 103,000
Stockholders' Equity Note, Stock Split, Conversion Ratio						6.5810
Convertible Preferred Stock, Shares Issued upon Conversion					29,794,359	29,794,359
Junior Series A convertible preferred
Preferred Units, Preferred Partners' Capital Account [Abstract]
Number of preferred units authorized				6,437,500
Issuance of units (in shares)				6,437,500
Gross cash proceeds from issuance \| $				$ 0
Number of license agreements for the development and commercialization of products received for issuance of preferred units \| item				4
Series B Preferred Stock [Member]
Preferred Units, Preferred Partners' Capital Account [Abstract]
Price per unit \| $ / shares		$ 1.4428
Issuance costs \| $		$ 400
Preferred Stock, Shares Authorized		86,639,279
Proceeds from Issuance of Preferred Stock and Preference Stock \| $		$ 124,600
First tranche, August 2017 \| Series A Convertible Preferred Units
Preferred Units, Preferred Partners' Capital Account [Abstract]
Number of preferred units authorized				13,200,001
Gross cash proceeds from issuance \| $				$ 13,200
Second tranche, April 2018 \| Series A Convertible Preferred Units
Preferred Units, Preferred Partners' Capital Account [Abstract]
Number of preferred units authorized			50,399,999
Gross cash proceeds from issuance \| $			$ 50,400
Third tranche, March 2019 \| Series A Convertible Preferred Units
Preferred Units, Preferred Partners' Capital Account [Abstract]
Number of preferred units authorized		39,400,000
Gross cash proceeds from issuance \| $		$ 39,400

Equity-Based Compensation - 2018 Equity Plan (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
	Mar. 19, 2019	Sep. 30, 2019	Dec. 31, 2018	Jan. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive units issued		3,208,491
Incentive units \| 2018 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units authorized			3,008,645	2,738,929
Incentive units issued			3,290,929
Incentive units cancelled			385,361
Increase in number of units			269,716
Incentive units available for issuance			103,077
unrecognized compensation			$ 2.5
Share compensation recognition period			3 years 6 months
Incentive units \| 2018 Equity Incentive Plan \| Employee and Non employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive units issued	148,415

Equity-Based Compensation - 2019 Equity Plan (Details) - Options - 2019 Stock Option and Incentive Plan - shares	Sep. 30, 2019	Jul. 29, 2019	Jun. 04, 2019	Mar. 29, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units authorized		6,700,197	5,382,828	5,292,355
Number of restricted shares issuable	2,892,998
Number of common stock issuable	3,023,714

Equity-Based Compensation - 2019 Equity Incentive Plan (Details) - shares		1 Months Ended	9 Months Ended
	Aug. 30, 2019	Jun. 30, 2019	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years	4 years
Employee and Non employee \| Equity Incentive Plan 2019 \| Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive units available for issuance	3,537,225
Percentage of annual increase in the shares	5.00%
Vesting period	4 years
Shares available for future issuance			3,352,840

Equity-Based Compensation - 2019 Equity Stock Purchase Plan (Details) - 2019 Employee Stock Purchase Plan	Aug. 30, 2019 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance	442,153
Automatic increase in to shares authorized by the number of shares	663,229
Automatic increase in to shares authorized as percentage of outstanding stock	1.00%

Equity-Based Compensation - Stock options (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Number of Award
Incentive units issued			3,208,491
Option exercised			(392)
Outstanding at the end	3,208,099		3,208,099
Exercisable	259,837		259,837
Weighted Average Exercise Price
Granted (in dollars per share)			$ 4.30
Option exercised (in dollars per share)			2.30
Outstanding at the end (in dollars per share)	$ 4.30		4.30
Exercisable (in dollars per share)	$ 2.30		$ 2.30
Weighted Average Remaining Contractual Life and Aggregate Intrinsic Value
Outstanding at the end (in years)			9 years 7 months 6 days
Exercisable (in years)			9 years 7 months 6 days
Outstanding at the end (in dollars)	$ 55,756,761		$ 55,756,761
Exercisable (in dollars)	5,035,641		5,035,641
Stock compensation expense	788,000	$ 235,000	$ 2,159,000	$ 843,000
Options \| 2019 Stock Option and Incentive Plan
Weighted Average Remaining Contractual Life and Aggregate Intrinsic Value
Expected dividend yield			0.00%
Unrecognized compensation expense, options	$ 9,000,000		$ 9,000,000
Share compensation recognition period			4 years
Stock compensation expense			$ 900,000
Options \| 2019 Stock Option and Incentive Plan \| Minimum
Weighted Average Remaining Contractual Life and Aggregate Intrinsic Value
Risk-free interest rate			1.45%
Expected term			5 years 9 months
Expected volatility			68.10%
Options \| 2019 Stock Option and Incentive Plan \| Maximum
Weighted Average Remaining Contractual Life and Aggregate Intrinsic Value
Risk-free interest rate			2.47%
Expected term			6 years 3 months
Expected volatility			71.00%

Equity-Based Compensation- Restricted stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Weighted Average Grant Date Fair Valued
Stock compensation expense	$ 788	$ 235	$ 2,159	$ 843
Restricted stock subject to future vesting
Weighted Average Grant Date Fair Valued
Unrecognized compensation expense, options	$ 1,200		$ 1,200
Share compensation recognition period			3 years
Stock compensation expense			$ 1,300
Restricted stock subject to future vesting \| 2019 Stock Option and Incentive Plan
Number of Units
Outstanding at the beginning			2,503,744
Vested			(815,493)
Forfeited			(12,570)
Unvested and outstanding at the end	1,675,681		1,675,681
Weighted Average Grant Date Fair Valued
Outstanding at the beginning (in dollars per share)			$ 1.25
Vested (in dollars per share)			1.15
Forfeited (in dollars per share)			1.45
Unvested and outstanding at the end (in dollars per share)	$ 1.22		$ 1.22

Equity-Based Compensation - Equity-based compensation expense related to restricted stock and stock options (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total equity compensation expenses	$ 788	$ 235	$ 2,159	$ 843
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total equity compensation expenses	194	56	505	102
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total equity compensation expenses	$ 594	$ 179	$ 1,654	$ 741

Equity-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	9 Months Ended
	Jun. 30, 2019	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive units issued		3,208,491
Exercise price of option		$ 4.30
Service of CEO	4 years
Vesting period	4 years	4 years
CEO Performance Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, options		$ 1.2
Share compensation recognition period		3 years 8 months 1 day
Options \| CEO Performance Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive units issued	176,411
Exercise price of option	$ 7.50
Number of trading day on which average closing price is based	60 days
Average closing price	$ 28.49

License and Collaboration Agreements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development expenses	$ 10,745	$ 3,406	$ 30,373	$ 6,192
Pfizer \| License agreement \| Nirogacestat \| Maximum
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone Payments Under Agreement			232,500
Pfizer \| License agreement \| Mirdametinib \| Maximum
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone Payments Under Agreement			$ 229,800
Pfizer \| License agreement \| Junior Series A Convertible Preferred Units
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Preferred Stock, Shares Issued	6,437,500		6,437,500
BeiGene, Ltd \| clinical collaboration agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development expenses			$ 400		$ 800

Commitments and Contingencies (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Oct. 31, 2018	Aug. 31, 2018
Operating Leases
Lease term				5 years
Rent expense	$ 700	$ 200
Security Deposit			$ 500	$ 40,467
Prepaid Rent			$ 1,500
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Remainder of 2019	331
2020	1,344
2021	1,372
2022	1,297
2023	135
Total obligations	$ 4,479

Net Loss per Share and Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net Loss per Share and Unit
Net Loss attributable to common stockholder - basic and	$ (16,833)	$ (5,004)	$ (34,360)	$ (11,594)
Weighted average common units outstanding, basic and diluted	0	433,401	0	262,273
Weighted average common shares outstanding, basic and diluted	9,487,329		3,716,877
Net Loss per unit, basic and diluted	$ 0.00	$ (11.55)	$ 0.00	$ (44.20)
Net loss per share, basic and diluted	$ (1.77)		$ (9.24)

Net Loss per Share and Unit - potential common units not included in the calculation of the diluted net loss per unit and share (Details) - shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	4,883,780	2,637,674
Restricted stock subject to future vesting
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1,675,681	2,637,674
Common stock options issued and outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	3,208,099

Investment and Variable Interest Entity (Details) - USD ($) shares in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Income (Loss) from Equity Method Investments	$ (2,501,000)	$ (2,501,000)	$ 0
Series A Preferred Units \| Individual Two
Investment in Mapkure	$ 250,000	$ 250,000
Ownership Interest	1.80%	1.80%
Series A Preferred Units \| BeiGene, Ltd
Investment in Mapkure	$ 10,000,000	$ 10,000,000
Ownership Interest	71.40%	71.40%
MapKure [Member]
Preferred units purchased	1.0	1.0
Income (Loss) from Equity Method Investments		$ 2,500,000
MapKure [Member] \| Series A Preferred Units
Investment in Mapkure	$ 3,500,000	$ 3,500,000
Preferred units purchased	3.5	3.5
Ownership Interest	25.00%	25.00%
MapKure [Member] \| Series A Preferred Units \| Individual One
Investment in Mapkure	$ 4,000,000	$ 4,000,000
MapKure [Member] \| Series A Preferred Units \| Individual Two
Investment in Mapkure	$ 3,500,000	$ 3,500,000
Ownership Interest	38.90%	38.90%

Related Party Transactions (Details)	9 Months Ended		12 Months Ended
Related Party Transactions (Details)	Sep. 30, 2019 USD ($) director	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Related Party Transaction [Line Items]
Number of board members \| director	2
Director
Related Party Transaction [Line Items]
Consulting and BOD expenses			$ 287,079
IPO [Member] \| Director
Related Party Transaction [Line Items]
Consulting and BOD expenses	$ 216,417	$ 193,133