Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accrued Liabilities Current [Abstract]
Payroll and related benefits	$ 6,629	$ 9,265
Professional fees	1,171	1,064
Royalties	107	845
Income taxes payable		6,469
Other	2,343	3,052
Accrued Expenses, Total	$ 10,250	$ 20,695