Other Comprehensive Income (Loss) (Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of service cost	$ (130,473)	$ (119,990)
Reclassification adjustments	(11,552)	(10,489)
Total before tax	(28,528)	(24,682)
Reclassification out of Accumulated Other Comprehensive Income | Pension and other postretirement plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of service cost	1,676	993
Total before tax	1,676	993
Total before tax	(552)	(322)
Total net of tax	1,124	671
Reclassification out of Accumulated Other Comprehensive Income | Derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	1,677	1,724
Reclassification adjustments	1,677	1,724
Total before tax	(635)	(627)
Total net of tax	$ 1,042	$ 1,097