Debt (Details) (USD $)			3 Months Ended			6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Senior secured revolving credit facility Redetermination	Jun. 30, 2013 Senior Notes 10.25 Percent Due 2014	Dec. 31, 2012 Senior Notes 10.25 Percent Due 2014	Jun. 30, 2013 Low End of the Range Senior secured revolving credit facility	Jun. 30, 2013 Low End of the Range Senior secured revolving credit facility LIBOR	Jun. 30, 2013 Low End of the Range Senior secured revolving credit facility Prime	Jun. 30, 2013 High End of the Range Senior secured revolving credit facility	Jun. 30, 2013 High End of the Range Senior secured revolving credit facility LIBOR	Jun. 30, 2013 High End of the Range Senior secured revolving credit facility Prime	Jun. 30, 2013 Gross Senior Notes 10.25 Percent Due 2014
Debt obligations
Credit facility maximum borrowing base			$ 1,400,000,000
Lender commitments			1,200,000,000
Loans payable basis spread on variable rate							1.50%	0.50%		2.50%	1.50%
Line of credit facility, unused capacity, commitment fee (as a percent)						0.35%			0.50%
Outstanding borrowings under credit facility	646,000,000	562,900,000
Letters of credit issued under the credit facility			23,200,000
Remaining borrowing capacity available under the credit facility			530,800,000
Credit facility borrowing base number of additional yearly redeterminations (in redeterminations)			1
Senior Notes, Current				$ 203,704,000	$ 0							$ 205,300,000