Restructuring - Summary of Net Restructuring Charges Within Consolidated Statement of Operation (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Restructuring Cost And Reserve [Line Items]
Total restructuring charges	$ 400	$ 1,422	$ 871	$ 577
Cost of Revenue [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring charges			27
Research and Development [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring charges	(109)	1,265	78	333
General and Administrative [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring charges	$ 509	$ 157	$ 766	$ 244