Accumulated Other Comprehensive Income by Component (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), beginning balance	$ (66,084)
Other Comprehensive Income Loss before Reclassifications	65,853
Amount Reclassified from Accumulated Other Comprehensive Loss	2,843
Accumulated Other Comprehensive Income (Loss), ending balance	2,612
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), beginning balance	(75,737)
Other Comprehensive Income Loss before Reclassifications	51,371
Amount Reclassified from Accumulated Other Comprehensive Loss	3,036
Accumulated Other Comprehensive Income (Loss), ending balance	(21,330)
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), beginning balance	22,194
Other Comprehensive Income Loss before Reclassifications	14,482
Amount Reclassified from Accumulated Other Comprehensive Loss	(436)
Accumulated Other Comprehensive Income (Loss), ending balance	36,240
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), beginning balance	(12,541)
Other Comprehensive Income Loss before Reclassifications	0
Amount Reclassified from Accumulated Other Comprehensive Loss	243
Accumulated Other Comprehensive Income (Loss), ending balance	$ (12,298)