Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Balance at January 1,	$ 1,259	$ 1,982	$ 2,402
Additions based on tax positions related to the current year	500	50	50
Additions for tax positions of prior years	47	74	111
Reductions for tax positions of prior years	0	(94)	(524)
Settlements	(710)	(753)	(57)
Balance at December 31,	$ 1,096	$ 1,259	$ 1,982