Income Taxes - Schedule of Reconciliation of Uncertain Tax Position (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns Roll Forward
Balance as of January 1	$ 401	$ 1,024
Additions for tax positions taken in prior years	465
Statute expirations		(576)
Reductions of tax positions taken in prior years		(47)
Balance as of December 31	$ 866	$ 401