Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized tax benefits at the beginning of year	$ 390	$ 82	$ 23
Additions for tax positions of current year	83	95
Additions for tax positions of prior years	57	213	59
Reductions for settlements with taxing authorities	0
Reductions for lapses of the applicable statutes of limitations	(5)
Unrecognized tax benefits at the end of the year	$ 525	$ 390	$ 82