Commitments and Contingencies - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended				12 Months Ended
	Jan. 31, 2020	Aug. 31, 2018	Oct. 31, 2016	Jun. 30, 2016	Dec. 31, 2020	Dec. 31, 2019	Jan. 31, 2017
Carna Collaboration Agreement [Member]
Loss Contingencies [Line Items]
Upfront License Fee					$ 0.3
Agreement Amendment [Member]
Loss Contingencies [Line Items]
Securities issuance obligation						$ 10.5
Changes in fair value					1.5
Asset Purchase Agreement [Member]
Loss Contingencies [Line Items]
Upfront payment paid		$ 3.0
Aggregate milestone payment					190.0
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					290.0
Milestone payment							$ 2.0
Upfront payment paid			$ 7.0
Additional milestone payment payable					319.5
CPF License Agreements [Member] | First patient first trial post amendment [Member]
Loss Contingencies [Line Items]
Milestone payment					$ 2.0
Carna License Agreement [Member]
Loss Contingencies [Line Items]
Upfront payment paid				$ 0.9