Accrued Expenses - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Payroll and employee-related costs	$ 10,135	$ 19,630
Professional services	6,225	7,935
Property and equipment purchases	699	688
Other	5,334	8,492
Total accrued expenses and other current liabilities	$ 22,393	$ 36,745