Significant Accounting Policies Other Noncurrent Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Future QF obligation, net	$ 134,324	$ 138,310
Pension and other employee benefits	120,122	131,887
Environmental	30,501	30,226
Customer advances	40,209	36,046
Asset retirement obligations	39,402	35,532	$ 21,435
Other	55,213	46,569
Total	$ 419,771	$ 418,570