Basis of Presentation and Accounting Policies Deferred Gains (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Deferred Gains	$ 122,841	$ 141,881	$ 135,909	$ 159,911
Increase (Decrease) in Deferred Charges	9,003	5,971
Amortization of Deferred Gains	2,850	1,667
Operating Expense [Member]
Amortization of Deferred Gains	17,369	16,897
Gain (Loss) on Asset Dispositions and Impairments, Net [Member]
Amortization of Deferred Gains	$ 1,852	$ 5,437