Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Disclosure Reconciliation Of Beginning And Ending Amount Of Unrecognized Tax Benefits [Abstract]
Balance at January 1	$ 2,874	$ 3,223
Additions based on tax positions related to the current year	2	1
Additions for tax positions of prior years	2
Reductions in prior year tax positions		(350)
Balance at December 31	$ 2,878	$ 2,874