Income Taxes - Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at January 1	$ 9,300	$ 8,256
Additions based on tax positions related to the current year	1,354	1,061	$ 969
Additions for tax positions of prior years	1,624	233	542
Reductions for tax positions of prior years	(148)	(192)	(80)
Settlement of tax audits	0	(33)	0
Reductions due to lapsed statute of limitations	(298)	(25)	(265)
Balance at December 31	$ 11,832	$ 9,300	$ 8,256