Income Taxes - Schedule of Gross Unrecognized Tax Benefits (Excluding Interest and Penalties) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Beginning Balance	$ 23,676	$ 19,400
Additions for current year tax positions	170	787
Increases for prior year tax positions	1,653	3,498
Settlements of prior year tax positions	(1,499)
Expiration of statutes	(2,649)	(9)
Ending Balance	$ 21,351	$ 23,676