Stock Based Compensation - Classification of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense included in total expenses	$ 9,480	$ 17,894
Capitalized stock-based compensation costs	(327)	(242)
Research and Development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	2,599	10,137
Selling, General and Administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 6,881	$ 7,757

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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