Income Taxes - Summary of Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Gross unrecognized tax benefits at beginning of year	$ 1,280	$ 1,158
Gross decreases in tax positions for prior years	(7)
Gross increases in tax positions for current year	171	490
Settlements		(100)
Lapse of statute of limitations	(351)	(268)
Gross unrecognized tax benefits at end of year	$ 1,093	$ 1,280