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Summary of Significant Accounting Policies (Adoption of New Accounting Standards) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase to cash flows provided by operating activities	$ (24,128)	$ 101,543	$ 29,489
Decrease to cash flows provided by investing activities	(778,859)	(263,071)	(465,028)
Decrease to cash flows provided by finaning activities	457,939	41,480	877,655
Impact of Adoption on Consolidated Financial Statements
Other investments	304,275	321,241		$ 397,110
Total assets	5,014,277	4,731,078		4,806,947
Retained earnings (deficit)	(2,472,061)	(2,470,564)		(2,394,695)
Total equity	$ 1,064,115	914,249	1,059,684	990,118	$ 1,101,330
ASU No. 2016-15
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase to cash flows provided by operating activities		20,800	7,300
Decrease to cash flows provided by finaning activities		20,800	7,300
ASU No. 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase to cash flows provided by operating activities		600	700
Decrease to cash flows provided by investing activities		$ 6,400	$ 1,500
ASU No. 2017-05 \| Impact from ASU
Impact of Adoption on Consolidated Financial Statements
Other investments				75,869
Total assets				75,869
Retained earnings (deficit)				75,869
Total equity				$ 75,869