Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Unrealized loss on derivatives	$ 0	$ 3,200
Net operating loss carryforwards	116,374	118,134
Percentage depletion carryover	1,624	1,582
Basis increase related to the San Mateo transaction	0	18,382
Other	9,115	0
Total deferred tax assets	127,113	141,298
Valuation allowance on deferred tax assets	(6,519)	(89,482)
Total deferred tax assets, net of valuation allowance	120,594	51,816
Deferred tax liabilities
Unrealized gain on derivatives	10,468	0
Property and equipment	(100,634)	(40,568)
Other	(2,256)	(11,248)
Total deferred tax liabilities	(113,358)	(51,816)
Net deferred tax assets	$ 7,236	$ 0