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Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Deferred tax assets:    
Net operating loss carryforward $ 879,339 $ 581,324
Divestiture contract obligation 132,352 0
Deferred compensation 16,635 16,815
Equity compensation 5,445 7,188
Asset retirement obligation 18,923 60,064
Interest expense carryover 15,757 18,035
Lease deferred tax assets 16,070 16,450
Cumulative mark-to-market loss 2,607 0
Other 12,082 11,072
Valuation allowances:    
Total deferred tax assets 720,191 520,122
Deferred tax liabilities:    
Depreciation and depletion (839,869) (639,581)
Cumulative mark-to-market gain 0 (25,957)
Lease deferred tax liabilities (15,058) (14,780)
Other (531) 0
Total deferred tax liabilities (855,458) (680,318)
Net deferred tax liability (135,267) (160,196)
Federal    
Valuation allowances:    
Valuation allowances (152,499) (32,530)
State, net of federal benefit    
Valuation allowances:    
Valuation allowances $ (226,520) $ (158,296)