Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforward	$ 581,324	$ 542,847
Deferred compensation	16,815	19,844
Equity compensation	7,188	8,152
AMT credits and other credits	0	3,296
Asset retirement obligation	60,064	78,126
Interest expense carryover	18,035	19,444
Lease deferred tax assets	16,450	0
Other	11,072	11,048
Valuation allowances:
Total deferred tax assets	520,122	562,410
Deferred tax liabilities:
Depreciation and depletion	(639,581)	(1,207,784)
Cumulative mark-to-market gain	(25,957)	(21,294)
Lease deferred tax liabilities	(14,780)	0
Total deferred tax liabilities	(680,318)	(1,229,078)
Net deferred tax liability	(160,196)	(666,668)
Federal
Valuation allowances:
Valuation allowances	(32,530)	(18,975)
State, net of federal benefit
Valuation allowances:
Valuation allowances	$ (158,296)	$ (101,372)