Significant Accounting Policies Other Noncurrent Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Pension and other employee benefits	$ 128,853	$ 125,809
Future QF obligation, net	92,937	102,260
Customer advances	56,870	50,089
Asset retirement obligations	42,449	40,659	$ 39,286
Environmental	27,741	28,741
Other	38,302	52,264
Total Noncurrent Liabilities	$ 387,152	$ 399,822