Income Taxes - Components of Provision for Income Taxes (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current
Federal
State	341	49	467
Total current tax expense	341	49	467
Deferred
Federal	19,707	(104,227)	(172)
State	6,982	(28,250)	218
Total deferred tax expense (benefit)	26,689	(132,477)	46
Income tax expense (benefit)	$ 27,030	$ (132,428)	$ 513