Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Oct. 01, 2016	Dec. 31, 2018	Dec. 31, 2017
Accounts receivable and other receivables
Reserves deducted from asset accounts:
Balance at Beginning of Year	$ 0		$ 0	$ 0
Additions (Reductions) Charged to Costs and Expenses	0			0
Charged to Other Accounts	0			0
Deductions	0			0
Balance at End of Year	0	$ 0	0	0
Current assets — supplies and inventory
Reserves deducted from asset accounts:
Balance at Beginning of Year	0		261	0
Additions (Reductions) Charged to Costs and Expenses	0		1,247	365
Charged to Other Accounts	0		0	(17)
Deductions	0		860	87
Balance at End of Year	0	0	648	261
Deferred income taxes
Reserves deducted from asset accounts:
Balance at Beginning of Year	1,033,982		610,571	1,021,553
Additions (Reductions) Charged to Costs and Expenses	(12,429)		(79,959)	(410,982)
Charged to Other Accounts				0
Deductions	0			0
Balance at End of Year	1,021,553	1,033,982	$ 530,612	$ 610,571
Predecessor | Accounts receivable and other receivables
Reserves deducted from asset accounts:
Balance at Beginning of Year	0	7,842
Additions (Reductions) Charged to Costs and Expenses		0
Charged to Other Accounts		0
Deductions		7,842
Balance at End of Year		0
Predecessor | Current assets — supplies and inventory
Reserves deducted from asset accounts:
Balance at Beginning of Year	0	5,991
Additions (Reductions) Charged to Costs and Expenses		844
Charged to Other Accounts		(5,060)
Deductions		1,775
Balance at End of Year		0
Predecessor | Deferred income taxes
Reserves deducted from asset accounts:
Balance at Beginning of Year	$ 1,033,982	1,135,399
Additions (Reductions) Charged to Costs and Expenses		(101,417)
Charged to Other Accounts		0
Deductions		0
Balance at End of Year		$ 1,033,982