Discontinued Operations and Assets Held for Sale (Major Categories of Assets and Liabilities Reflected as Held for Sale) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets
Total current assets associated with assets held for sale	$ 128,415	$ 173,865	[1]
Non-current assets
Total non-current assets associated with assets held for sale	0	1,545,008	[1]
Current liabilities
Accounts payable	8,563	203,236
Other accrued liabilities	448	55,273
Current maturities of long-term debt (finance lease)	696	9,915
Taxes payable	752	18,034
Long-term debt (finance lease)	7,420	0
Asset retirement obligation	235	0
Total current liabilities associated with assets held for sale	18,114	286,458	[1]
Non-current liabilities
Long-term debt	0	117,816
Asset retirement obligation	0	274,904
Total non-current liabilities associated with assets held for sale	0	392,720	[1]
Discontinued Operations, Held-for-sale or Disposed of by Sale
Current assets
Cash	25,307	44,669
Accounts receivable	3,859	103,158
Inventories	406	7,887
Prepaid expenses and other	1,847	18,151
Property, Plant, and Equipment, net	87,556	0
Deferred income taxes and other assets	9,440	0
Total current assets associated with assets held for sale	128,415	173,865
Non-current assets
Property, Plant, and Equipment, net	0	1,325,431
Non-current deferred income taxes and other assets	0	219,577
Total non-current assets associated with assets held for sale	$ 0	$ 1,545,008

[1] Reclassified to conform to current presentation (see Note A).