Income Taxes - Components of Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Current	$ (1,080)	$ 78
Deferred:
Federal	4,023	(247)	$ (2,728)
Change in valuation allowance	(4,023)	247	1,966
Total deferred			(762)
Total income tax (benefit) expense	$ (1,080)	$ 78	$ (762)