Income Taxes - Reconciliation of Uncertain Tax Positions (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Beginning balance of uncertain tax positions	$ 10,441		$ 11,450
Additions related to current year tax positions	0	$ 0	0
Reductions related to prior year tax positions	(506)	0	0
Settlements	0	(593)	(694)
Lapse of statute of limitations	(69)	(416)	$ 0
Ending balance of uncertain tax positions	$ 9,866	$ 10,441