Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	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	0
Charged to Other Accounts	10,636	0	0
Deductions	0	0	0
Balance at End of Year	10,636	0	0
Current assets — supplies and inventory
Reserves deducted from asset accounts:
Balance at Beginning of Year	648	261	0
Additions (Reductions) Charged to Costs and Expenses	1,737	1,247	365
Charged to Other Accounts	(35)	0	(17)
Deductions	134	860	87
Balance at End of Year	2,216	648	261
Deferred income taxes
Reserves deducted from asset accounts:
Balance at Beginning of Year	530,612	610,571	1,021,553
Additions (Reductions) Charged to Costs and Expenses	(24,296)	(79,959)	(410,982)
Charged to Other Accounts	0	0
Deductions	0	0	0
Balance at End of Year	$ 506,316	$ 530,612	$ 610,571