Commitments and Contingencies - Additional Information (Detail) $ / shares in Units, $ in Millions	1 Months Ended				3 Months Ended	12 Months Ended
	Jan. 31, 2020 $ / shares shares	Aug. 31, 2018 USD ($)	Oct. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2020 USD ($) Payments shares	Dec. 31, 2019 USD ($)	Jan. 31, 2017 USD ($)
Carna License Agreement [Member]
Loss Contingencies [Line Items]
Aggregate milestone payment					$ 270.0
Milestone payment					$ 4.0
Upfront payment paid				$ 0.9
Number of milestone payments recorded | Payments					0
CPF License Agreements [Member]
Loss Contingencies [Line Items]
Aggregate milestone payment					$ 19.5
Milestone payment							$ 2.0
Upfront payment paid			$ 7.0
Additional milestone payment payable					319.5
CPF License Agreements [Member] | Phase One Clinical Trial [Member]
Loss Contingencies [Line Items]
Milestone payment					7.5
CPF License Agreements [Member] | Phase Two Clinical Trial [Member]
Loss Contingencies [Line Items]
Milestone payment					12.0
Asset Purchase Agreement [Member]
Loss Contingencies [Line Items]
Upfront payment paid		$ 3.0
Aggregate milestone payment					190.0
Expense included research and development cost						$ 10.5
Additional Exepense included Research and development cost					$ 1.5
Asset Purchase Agreement [Member] | Gilead [Member]
Loss Contingencies [Line Items]
Stock issued, shares | shares	725,283
Number of securitites called by warrants and rights | shares	725,283
Asset Purchase Agreement Amendment [Member] | Gilead [Member]
Loss Contingencies [Line Items]
Stock issued, shares | shares	725,283
Number of securitites called by warrants and rights | shares					725,283
Excercise price of warrants or rights | $ / shares	$ 13.20