Income Taxes - Summary of Changes in Liability Related to 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 benefit liability, Beginning Balance	$ 4,357	$ 4,755	$ 5,740
New positions	653
Prior period positions:
Increases	491	939	175
Decreases	(539)	(415)
Increases from current period positions	692	615	184
Lapse of statute of limitations	(781)	(1,290)	(1,114)
Other	(228)	(247)	(230)
Unrecognized tax benefit liability, Ending Balance	$ 4,645	$ 4,357	$ 4,755