Segment Information - Reconciliation of Net Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue from External Customer [Line Items]
Segment Adjusted EBITDA	$ 28,266	$ 182,241		$ 98,090	$ 369,294
Other revenues	163,701	397,613		390,421	775,903
Cost of other revenues	(7,642)	(8,019)		(15,203)	(15,764)
Depreciation and depletion	(22,156)	(25,678)		(50,848)	(47,911)
Selling, general and administrative	(8,457)	(10,783)		(16,913)	(19,688)
Loss on early extinguishment of debt	0	0	$ (9,800)	0	(9,756)
Other income	0	17,543		1,822	17,543
Interest expense, net	(8,255)	(6,951)		(15,788)	(15,543)
Income tax benefit (expense)	4,425	(33,056)		1,184	(61,040)
Net income (loss)	(9,161)	125,481		12,384	235,928
Other revenues
Revenue from External Customer [Line Items]
Other revenues	$ 4,658	$ 10,184		$ 10,040	$ 18,793