The Company and Subsequent Events - Summary of Reconciliation of Beginning and Ending Restructuring Liability (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Restructuring Cost And Reserve [Line Items]
Balance, beginning of period
Additions, charged to costs	$ 5,818	$ 12,898
Payments		(10,809)
Balance, end of period	2,089	2,089
One-Time Employee Termination Benefit Costs
Restructuring Cost And Reserve [Line Items]
Balance, beginning of period
Additions, charged to costs		6,550
Payments		(5,395)
Balance, end of period	1,155	1,155
Contract Termination Costs
Restructuring Cost And Reserve [Line Items]
Balance, beginning of period
Additions, charged to costs		1,035
Payments		(101)
Balance, end of period	$ 934	934
Consulting Costs
Restructuring Cost And Reserve [Line Items]
Additions, charged to costs		2,956
Payments		(2,956)
Asset Disposal Costs
Restructuring Cost And Reserve [Line Items]
Additions, charged to costs		2,357
Payments		$ (2,357)