Tax Effects of Temporary Differences that Give Rise to Significant Portions of Deferred Income Tax Assets and Liabilities (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2013
Dec. 31, 2012
Current deferred income tax assets:    
Derivative financial instruments $ 3,914 $ 8,706
Asset retirement obligation 675 1,275
Equity compensation 2,924  
Other 817 776
Total current assets 8,330 10,757
Long term deferred income tax assets (liabilities):    
Derivative financial instruments   2,885
Net operating loss carryovers 62,457 27,565
Asset retirement obligation 11,161 5,874
Startup and organization costs 158 178
Deferred acquisition costs 45 45
Percentage depletion 1,323 1,118
Property and equipment costs (110,566) (140,048)
Equity compensation 1,233 2,551
Other (635) (2,082)
Total long term liabilities (34,824) (101,914)
Net deferred tax liability $ (26,494) $ (91,157)