Accumulated Other Comprehensive Income by Component (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), beginning balance	$ (60,597)	$ (66,084)	$ (64,035)
Other Comprehensive Income Loss before Reclassifications	3,463	7,383	4,161
Amount Reclassified from Accumulated Other Comprehensive Loss	972	2,539	3,712
Accumulated Other Comprehensive Income (Loss), ending balance	(56,162)	(56,162)	(56,162)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), beginning balance	(74,198)	(75,737)	(75,403)
Other Comprehensive Income Loss before Reclassifications	0	0	(1,331)
Amount Reclassified from Accumulated Other Comprehensive Loss	1,065	2,604	3,601
Accumulated Other Comprehensive Income (Loss), ending balance	(73,133)	(73,133)	(73,133)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), beginning balance	26,030	22,194	23,994
Other Comprehensive Income Loss before Reclassifications	3,463	7,383	5,492
Amount Reclassified from Accumulated Other Comprehensive Loss	(158)	(242)	(151)
Accumulated Other Comprehensive Income (Loss), ending balance	29,335	29,335	29,335
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), beginning balance	(12,429)	(12,541)	(12,626)
Other Comprehensive Income Loss before Reclassifications	0	0	0
Amount Reclassified from Accumulated Other Comprehensive Loss	65	177	262
Accumulated Other Comprehensive Income (Loss), ending balance	$ (12,364)	$ (12,364)	$ (12,364)