Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Oct. 01, 2016	Dec. 31, 2017	Dec. 31, 2015
Income Tax Examination [Line Items]
Provision for (benefit from) income taxes	$ 1,156		$ (35,255)
Successor
Income Tax Examination [Line Items]
Income tax provision (benefit) at statutory rate	12,112		71,118
Percentage depletion allowance	(4,292)		(31,255)
State taxes, net of effect of federal taxes	633		7,002
Reversal of cancellation of indebtedness income	0		0
Worthless stock deduction	0		0
Change in valuation allowance	(7,655)		(410,983)
Impact of Tax Cuts and Jobs Act of 2017	0		332,345
Other, net	358		(3,482)
Provision for (benefit from) income taxes	$ 1,156		$ (35,255)
Predecessor
Income Tax Examination [Line Items]
Income tax provision (benefit) at statutory rate		$ 433,109		$ (1,150,283)
Percentage depletion allowance		(3,681)		(19,035)
State taxes, net of effect of federal taxes		(46,122)		(76,445)
Reversal of cancellation of indebtedness income		(1,493,162)		0
Worthless stock deduction		(80,077)		0
Change in valuation allowance		1,185,326		865,146
Impact of Tax Cuts and Jobs Act of 2017		0		0
Other, net		(19)		7,237
Provision for (benefit from) income taxes		$ (4,626)		$ (373,380)