Accumulated Other Comprehensive Income (Loss) (AOCI balances) (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	$ 2,915,145
Other Comprehensive Income, Net of Tax	10,812	$ 18,282
Accumulated Other Comprehensive Income (Loss), ending balance	2,884,913
AOCI Including Portion Attributable to Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	535,555
Reclassification from accumulated other comprehensive income to retained earnings as a result of adoption of new guidance	(194,889)
Other comprehensive income before reclassifications	11,753
Net amount reclassified from accumulated other comprehensive income (loss)	(941)
Other Comprehensive Income, Net of Tax	10,812
Accumulated Other Comprehensive Income (Loss), ending balance	351,478
Cumulative Foreign Currency Translation Adjustment [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	6,314
Reclassification from accumulated other comprehensive income to retained earnings as a result of adoption of new guidance	0
Other comprehensive income before reclassifications	11,564	13,668
Net amount reclassified from accumulated other comprehensive income (loss)	0
Other Comprehensive Income, Net of Tax	11,564
Accumulated Other Comprehensive Income (Loss), ending balance	17,878
Unrealized Gain on Available-for-Sale Securities [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	194,889
Reclassification from accumulated other comprehensive income to retained earnings as a result of adoption of new guidance	(194,889)
Other comprehensive income before reclassifications	0	5,735
Net amount reclassified from accumulated other comprehensive income (loss)	0
Other Comprehensive Income, Net of Tax	0
Accumulated Other Comprehensive Income (Loss), ending balance	0
Unrealized Gain on Pensions and Other Postretirement Plans [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	334,536
Reclassification from accumulated other comprehensive income to retained earnings as a result of adoption of new guidance	0
Other comprehensive income before reclassifications	0
Net amount reclassified from accumulated other comprehensive income (loss)	(943)	(1,022)
Other Comprehensive Income, Net of Tax	(943)	(1,022)
Accumulated Other Comprehensive Income (Loss), ending balance	333,593
Cash Flow Hedge [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	(184)
Reclassification from accumulated other comprehensive income to retained earnings as a result of adoption of new guidance	0
Other comprehensive income before reclassifications	189
Net amount reclassified from accumulated other comprehensive income (loss)	2
Other Comprehensive Income, Net of Tax	191	$ (99)
Accumulated Other Comprehensive Income (Loss), ending balance	$ 7