Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets
Unrealized loss on derivatives	$ 3,200	$ 8,734
Net operating loss carryforwards	118,134	137,757
Alternative minimum tax carryforward	0	8,633
Percentage depletion carryover	1,582	2,595
Property and equipment	0	44,391
Basis increase related to the San Mateo transaction	18,382	0
Total deferred tax assets	141,298	202,110
Valuation allowance on deferred tax assets	(89,482)	(190,255)
Total deferred tax assets, net of valuation allowance	51,816	11,855
Deferred tax liabilities
Property and equipment	40,568	0
Other	(11,248)	(11,855)
Total deferred tax liabilities	(51,816)	(11,855)
Net deferred tax liabilities	$ 0	$ 0