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
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of year	$ 15,190	$ 15,815	$ 17,581
Additions based on tax positions related to the current year	2,644	2,184	1,969
Additions for tax positions of prior years	1,511	1,317	61
Reductions for tax positions for prior years	(430)	(1,369)	(3,152)
Reduction for lapse in statute of limitations	(3,917)	(2,516)	(425)
Settlements	(301)	(241)	(219)
Balance at end of year	$ 14,697	$ 15,190	$ 15,815