Income Taxes - Summary of Reconciliation of Beginning and Ending Amounts of Unrecognized Tax Benefits, Excluding Interest and Penalties (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Beginning balance	$ 4,741	$ 5,724	$ 3,834
Additions for tax positions of prior years	1,404	179	2,516
Reductions for tax positions of prior years	(490)	(1,162)	(626)
Ending balance	$ 5,655	$ 4,741	$ 5,724