Income Taxes - Components of (Benefit) Provision for Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal		$ (615)	$ (117)	$ 948
State		314	246	399
Foreign		57	84	41
Total current (benefit) provision		(244)	213	1,388
Deferred:
Federal		131	(2,545)	(4,624)
State		238	(63)	0
Foreign		4	4	18
Total deferred benefit		373	(2,604)	(4,606)
Provision (benefit) for income taxes	$ (3,218)	$ 129	$ (2,391)	$ (3,218)