Federal Income Taxes - Schedule of Income Tax Expense (Benefit) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Components Of Income Tax Expense Benefit [Line Items]
Current federal income tax expense	$ 0	$ 0	$ 33,401
Provision for doubtful federal income tax receivable			(46,428)
Deferred federal income tax (benefit) expense
Federal income tax benefit			$ (13,027)