Commitments and Contingencies - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended				3 Months Ended	9 Months Ended	12 Months Ended
	Jan. 31, 2020	Aug. 31, 2018	Oct. 31, 2016	Jun. 30, 2016	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019	Jan. 31, 2017
Loss Contingencies [Line Items]
Collaboration revenue					$ 100	$ 100
Deferred Revenue					200	200
Carna Collaboration Agreement [Member]
Loss Contingencies [Line Items]
Upfront License Fee						300
Collaboration revenue					100
Deferred Revenue					200	200
Asset Purchase Agreement [Member]
Loss Contingencies [Line Items]
Upfront payment paid		$ 3,000
Aggregate milestone payment						190,000
Expense included research and development cost							$ 10,500
Additional expense included research and development cost						1,500
Asset Purchase Agreement Amendment [Member] | Gilead [Member]
Loss Contingencies [Line Items]
Stock issued, shares	725,283
Number of securities called by warrants and rights	725,283
Excercise price of warrants or rights	$ 13.20
CPF License Agreements [Member]
Loss Contingencies [Line Items]
Aggregate milestone payment						19,500
Upfront payment paid			$ 7,000
Milestone payment								$ 2,000
Additional milestone payment payable						319,500
CPF License Agreements [Member] | Phase 1 Clinical Trial in the US [Member]
Loss Contingencies [Line Items]
Milestone payment					7,500	7,500
CPF License Agreements [Member] | Phase Two Clinical Trial [Member]
Loss Contingencies [Line Items]
Milestone payment					$ 12,000	$ 12,000
Carna License Agreement [Member]
Loss Contingencies [Line Items]
Upfront payment paid				$ 900