Discontinued Operations and Assets Held for Sale (Major Categories of Assets and Liabilities Reflected as Held for Sale) (Details) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total current assets associated with assets held for sale		$ 1,879,568	$ 173,865	[1]
Total non-current assets associated with assets held for sale	[1]		1,545,008
Total current liabilities associated with assets held for sale		819,694	286,458	[1]
Total non-current liabilities associated with assets held for sale	[1]		392,720
Discontinued Operations, Held-for-sale or Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash		93,072	44,669
Accounts receivable		98,268	103,158
Inventories		8,881	7,887
Prepaid expenses and other		28,248	18,151
Property, Plant and Equipment, net		1,316,985
Deferred income taxes and other assets		214,103
Operating lease asset		120,011
Total current assets associated with assets held for sale		1,879,568	173,865
Property, Plant and Equipment, net			1,325,431
Deferred income taxes and other assets			219,577
Total non-current assets associated with assets held for sale			1,545,008
Accounts payable		209,012	203,236
Other accrued liabilities		50,524	55,273
Current maturities of long-term debt		10,067	9,915
Taxes payable		35,032	18,034
Current operating lease obligations		45,982
Total current liabilities associated with assets held for sale		819,694	286,458
Long-term debt		115,264	117,816
Asset retirement obligation		279,784	274,904
Non-current operating lease liabilities		$ 74,029
Total non-current liabilities associated with assets held for sale			$ 392,720

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