Restructuring Activities - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restructuring Cost And Reserve [Line Items]
Restructuring expenses		$ 4,783	$ 1,289
Payments for restructuring	$ 400	5,638	996
Accrued restructuring expenses	$ 921	66	921	$ 628
One-time Termination Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses		4,800	1,300
One-time Termination Benefits [Member] | Research and Development Expense [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses		2,000	1,000
One-time Termination Benefits [Member] | General and Administrative Expense [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses		$ 2,800	$ 300
November 2018 Corporate Restructuring [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring activity, announcement date		Nov. 07, 2018