Components of Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Expenses [Line Items]
Current income tax expense (benefit), Federal	$ 2,519	$ 9,326	$ 13,674
Current income tax expense (benefit), State	136	828	2,368
Current income tax expense (benefit), Total	2,655	10,154	16,042
Deferred income tax expense (benefit), Federal	5,589	(2,280)	(144,771)
Deferred income tax expense (benefit), State	117	(931)	(6,266)
Deferred income tax expense (benefit), Total	5,706	(3,211)	(151,037)
Income tax expense (benefit)	$ 8,361	$ 6,943	$ (134,995)