Quarterly report pursuant to Section 13 or 15(d)

Income Taxes (Deferred Tax Assets and Liabilities) (Details)

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Income Taxes (Deferred Tax Assets and Liabilities) (Details) (USD $)
In Thousands, unless otherwise specified
 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Dec. 31, 2011
Deferred tax asset:      
Federal net operating loss carryforward $ 88,987   $ 86,551
Statutory depletion carryforward 7,600   7,032
Alternative minimum tax credit carryforward 208   208
Asset retirement obligations 3,496   3,552
Other 7,064   9,182
Deferred tax asset before valuation allowance 107,355   106,525
Less: Valuation allowance 0   0
Total deferred tax asset 107,355   106,525
Deferred tax liability:      
Crude oil and natural gas properties 41,325   38,534
Acquired assets (see Note 9) 2,065   2,248
Total deferred tax liability 43,390   40,782
Net deferred tax asset $ 63,965   $ 65,743
Effective tax rate (as a percent) 30.00% 0.00%