Income Taxes - Effective Income Tax Rate on Pretax Earnings (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax benefit (expense) computed at U.S. federal statutory rate									$ 90,070	$ 48,290	$ (47,784)
Decrease (increase) resulting from:
Statutory depletion									4,679	12,090	20,259
Goodwill impairment									0	(29,157)	0
Prior year tax return reconciliation									3,121	530	219
State income taxes, net of federal benefit									9,486	2,592	(2,267)
Adjustment to deferred taxes from the Tax Act rate reduction									0	0	35,772
Equity compensation									(6,440)	(653)	2,602
Other, net									(1,765)	(4,560)	(121)
Income tax benefit	$ 91,892	$ 7,671	$ (2,384)	$ 1,972	$ 37,938	$ 1,547	$ (2,832)	$ (7,521)	$ 99,151	$ 29,132	$ 8,680