Quarterly report pursuant to Section 13 or 15(d)

Consolidated Balance Sheets (Parenthetical)

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Consolidated Balance Sheets (Parenthetical) (USD $)
In Thousands, except Share data, unless otherwise specified
6 Months Ended 12 Months Ended
Jun. 30, 2013
Dec. 31, 2012
Statement of Financial Position [Abstract]    
Capitalized costs of oil and natural gas properties excluded from amortization $ 872,113 $ 626,295
Equity investments attributable to fair value option $ 198,662 $ 151,317
Preferred stock, par value (usd per share) $ 0.01 $ 0.01
Preferred stock, shares authorized (shares) 5,000,000 5,000,000
Preferred stock dividend rate 12.00% 12.00%
Temporary Equity, Shares Authorized (shares) 30,000 30,000
Preferred stock Series A, issued (shares) 0 0
Preferred stock Series A, outstanding (shares) 0 0
Common stock, par value (usd per share) $ 0.01 $ 0.01
Common Stock, Shares Authorized (shares) 100,000,000 100,000,000
Common Stock, Shares, Issued (shares) 77,547,606 67,527,386
Common Stock, Shares, Outstanding (shares) 77,547,606 67,527,386