Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)		3 Months Ended	12 Months Ended
	Jan. 01, 2018	Mar. 31, 2016	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Line Items]
Maximum maturity days for cash equivalents			90 days
Restricted investments			$ 1,400,000	$ 1,400,000
Impairment losses on long lived assets			0
Upfront collaboration/license fee		$ 120,000,000	$ 120,000,000
Period of performance identifiable deliverables			10 years
Adoption of new revenue standard (ASC 606)				$ 26,857,000
Revenue related to sales-based royalties			$ 0
Revenue related to milestone payments			$ 0
Minimum percentage of likelihood of tax benefit being realized upon settlement			50.00%
ASU 2014-09 [Member]
Accounting Policies [Line Items]
Adoption of new revenue standard (ASC 606)	$ 26,857,000
Laboratory Equipment [Member]
Accounting Policies [Line Items]
Useful life of asset			5 years
Computer Equipment [Member]
Accounting Policies [Line Items]
Useful life of asset			3 years
Furniture and Office Equipment [Member]
Accounting Policies [Line Items]
Useful life of asset			3 years