Quarterly report pursuant to Section 13 or 15(d)

Basis of Presentation and Accounting Policies Deferred Gains (Details)

v3.8.0.1
Basis of Presentation and Accounting Policies Deferred Gains (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Deferred Gains $ 69,378 $ 78,192 $ 72,453 $ 82,423
Operating Expense [Member]        
Amortization of Deferred Gains 2,557 3,626    
Gain (Loss) on Asset Dispositions and Impairments, Net [Member]        
Amortization of Deferred Gains $ 518 $ 605