Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Current federal income tax expense (benefit)		$ (179)
Current state income tax expense (benefit)	$ (17)	(144)	$ 9
Deferred federal income tax expense (benefit)	1,290	(1,150)	(4,275)
Deferred state income tax expense (benefit)	1,111	468	(452)
Income Tax Expense (Benefit)	$ 2,384	$ (1,005)	$ (4,718)