Restructuring Activities- Additional Information (Detail) $ in Thousands		3 Months Ended				6 Months Ended		12 Months Ended
	Jul. 12, 2019 Employee	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Restructuring Cost And Reserve [Line Items]
Restructuring expenses					$ 0	$ 4,890	$ 0
Payments for restructuring			$ 3,800	$ 400	$ 200	4,755	$ 628	$ 900
Number of employees | Employee	0
Scenario, Forecast [Member]
Restructuring Cost And Reserve [Line Items]
Payments for restructuring		$ 1,100
One-time Termination Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses			4,600			4,900		1,300
One-time Termination Benefits [Member] | Research and Development Expense [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses			1,800			2,000		1,000
One-time Termination Benefits [Member] | General and Administrative Expense [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses			$ 2,800			$ 2,900		$ 300
November 2018 Corporate Restructuring [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring activity, announcement date						Nov. 07, 2018