Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Long-term restricted cash	$ 1,181	$ 1,181
Rent expense	2,900	$ 2,400	$ 3,000
Future minimum lease payments under non-cancelable operating leases
2018	3,790
2019	3,856
2020	3,860
2021	3,406
Thereafter	3,497
Total	$ 18,409