Stock-Based Compensation - Summary of Stock-Based Compensation Expense Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 34,342	$ 20,108	$ 83,981	$ 75,250
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	17,864	9,927	40,598	32,270
Selling, General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 16,478	$ 10,181	$ 43,383	41,192
Restructuring Charges [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense				$ 1,788