Taxes (Schedule of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Tax loss carryforwards	$ 271,405	$ 376,293	$ 1,135,000
Tax credit carryforwards	29,736	22,798
Investment in tax partnerships & corporations	308,653	604,914
Other	28,321	39,251
Gross deferred tax assets	638,115	1,043,256
Valuation allowance	(610,571)	(1,021,553)
Total deferred tax assets	27,544	21,703
Deferred tax liabilities:
Plant and equipment	3,674	7,332
Other	1,351	14,258
Total deferred tax liabilities	5,025	21,590
Net deferred tax asset	$ 22,519	$ 113