Income Taxes - Summary of Activity Related to Company's Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Beginning balance	$ 5,045	$ 8,330	$ 3,438
Additions based on tax positions related to the current year	622	1,023	557
Additions for tax positions of prior years	(8)	27	4,335
Reductions for tax positions of prior years		(4,335)
Ending balance	$ 5,659	$ 5,045	$ 8,330