Reconciliation of Total Amounts of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Beginning uncertain tax benefits	$ 1,633	$ 1,550	$ 2,487
Prior year—increases			120
Prior year—decreases	(20)		(762)
Current year—increases	121	83	144
Current year—decreases for lapses in statutes of limitations			(439)
Ending uncertain tax benefits	$ 1,734	$ 1,633	$ 1,550