Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Gross unrecognized tax benefits - beginning of the year	$ 1,832	$ 1,139
Gross increases related to prior year tax positions	1,830	394
Gross increases related to current year tax positions	290	488
Lapse of applicable statute of limitations	(125)	(189)
Gross unrecognized tax benefits - end of year	$ 3,827	$ 1,832