Significant Accounting Policy Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (392,556)	$ (315,598)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	(392,556)	(359,068)
Other Comprehensive Income (Loss), Net of Tax	(76,696)	(164,498)	$ 174,017
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	0	$ 43,470
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(61,730)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(14,966)
Postretirement Benefit Costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Net of Tax	(33,226)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(61,730)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	28,504
Cash Flow Hedging [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Net of Tax	(43,470)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ (43,470)