Income Taxes (Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income (loss) before income taxes	$ (2,411,567)	$ 103,229	$ 308,470
Income tax expense computed at the statutory federal income tax rate	(506,429)	21,678	64,779
State income tax expense (benefit), net of federal benefit	(11,827)	1,253	3,568
Equity based compensation	2,746	1,222	(494)
Non-deductible compensation	0	90	1,209
Non-deductible merger expenses	0	5,537	0
Statutory depletion carryforward	0	5,381	0
Other	(1,621)	140	168
Change in valuation allowance	639,185	0	(61,120)
Income tax expense	$ 122,054	$ 35,301	$ 8,110