Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating loss carryforwards	$ 76,213	$ 106,992
Statutory depletion carryforwards	9,913	9,809
Asset retirement obligations and other	22,518	21,249
Deferred tax assets, gross	108,644	138,050
Deferred tax liabilities:
Property and equipment	(178,714)	(240,520)
Net deferred tax liabilities	(70,070)	(102,470)
Components of net deferred tax liabilities:
Current assets	6,520	6,526
Non-current liabilities	(76,590)	(108,996)
Net deferred tax liabilities	$ (70,070)	$ (102,470)