Organization, Basis of Presentation and Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Schedule of Liabilities Measured at Fair Value on Recurring Basis

Liabilities measured at fair value on a recurring basis are as follows (in thousands):

			Fair Value Measurements at Reporting Date Using:
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of December 31, 2018:
Convertible promissory notes	$	1,950	$	—	$	—	$	1,950
As of September 30, 2019:
Warrant liabilities	$	107,373	$	—	$	—	$	107,373
Convertible promissory notes		95,229		—		—		95,229
Total	$	202,602	$	—	$	—	$	202,602

Schedule of Adjustment of Carrying Value to Their Estimated Fair Value

The Company adjusts the carrying value of its warrant liabilities and convertible promissory notes to their estimated fair value at each reporting date, with any related increases or decreases in the fair value recorded as change in fair value of warrant liabilities and change in fair value of convertible promissory notes, respectively, in the combined statements of operations.

Liability	At initial valuation date		Fair value as of September 30,		Fair value method at initial valuation date (and relative weighting)	Fair value method at as of September 30, 2019 (and relative weighting)	KEY unobservable inputs	Range
Takeda Warrants		47,894		107,373	Financing transactions (40%) Income approach (60%)	Financing transactions (70%) Income approach (30%)	Transaction prices per share Estimated time to liquidity Discount rate	$9.33 - $18.56 0.09 - 1.77 years 7.5%
May 2019 Notes		90,250		95,229	Financing transactions (40%) Income approach (60%)	Financing transactions (70%) Income approach (30%)	Estimated time to liquidity Volatility Discount rate	0.09 - 1.77 years 65% 22.6% - 25%

Schedule of Reconciliation of Liabilities Measured at Fair Value

The following table provides a reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs (in thousands):

	Warrant Liabilities		Convertible Promissory Notes
Balance at January 1, 2018	$	—	$	—
Issuance of convertible promissory notes		—		1,900
Change in fair value		—		50
Balance at December 31, 2018		—		1,950
Issuance of convertible promissory notes		—		90,750
Exchange of convertible promissory notes (Note 4)		—		(2,399	)
Issuance of warrants		48,313		—
Change in fair value		59,060		4,928
Balance at September 30, 2019	$	107,373	$	95,229

Schedule of Potentially Dilutive Securities from Computation of Diluted Net Loss Per Share

The following potentially dilutive securities were excluded from the computation of diluted net loss per share for the periods presented because their inclusion would have been antidilutive:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Warrants		7,588,000		—		7,588,000		—
Stock options		1,400,528		—		1,400,528		—
Shares subject to repurchase		4,550,428		—		3,342,544		—