Taxes (Schedule of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Tax loss carryforwards	$ 294,535	$ 307,615
Tax credit carryforwards	5,297	5,394
Investment in partnerships	190,418	193,217
Other	20,387	28,747
Gross deferred tax assets	510,637	534,973
Valuation allowance	(506,316)	(530,612)	$ (610,600)
Total deferred tax assets	4,321	4,361
Deferred tax liabilities:
Plant and equipment	2,063	3,037
Other	2,178	1,154
Total deferred tax liabilities	4,241	4,191
Net deferred tax asset	$ 80	$ 170