Stock-based Compensation - Summary of Allocated Stock-based Compensation Expense (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Feb. 24, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense		$ 1,976	$ 3,016	$ 5,971	$ 5,674
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense		262	744	481	1,269
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense		$ 1,714	$ 2,272	3,366	$ 4,405
Restructuring Charges [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 2,100			$ 2,124