Basis of Presentation and Accounting Policies Deferred Gains (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Deferred Gains	$ 81,691	$ 91,339	$ 82,423	$ 92,610
Amortization of Deferred Gains	0	1,697
Operating Expense [Member]
Amortization of Deferred Gains	7,242	7,367
Gain (Loss) on Asset Dispositions and Impairments, Net [Member]
Amortization of Deferred Gains	$ 1,210	$ 1,210