Accumulated Other Comprehensive Income Amounts Reclassified (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended				12 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Prior service benefit	$ 2,065		$ 1,369		$ 5,594		$ 4,169		$ 6,985		$ 5,610
Unrealized Losses on Available-for-Sale Securities included in Pre-Tax Income	0		0		0		0		0		313
Interest on long-term debt and revolving credit facility	(11,595)		(12,095)		(35,064)		(35,854)		(46,922)		(46,985)
Income tax expense	22,662		27,084		38,898		46,328		36,225		48,001
Net income (loss)	52,301		50,415		86,894		87,143		88,093		91,958
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net income (loss)	902		(972)		3,575		(2,539)		3,271		(3,712)
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Prior service benefit	2,065	[1]	1,369	[1]	5,594	[1]	4,169	[1]	6,985	[1]	5,610	[1]
Net Loss	(1,615)	[1]	(2,903)	[1]	(4,567)	[1]	(8,323)	[1]	(6,716)	[1]	(11,316)	[1]
Income (Loss) before income tax	450	[1]	(1,534)	[1]	1,027	[1]	(4,154)	[1]	269	[1]	(5,706)	[1]
Income tax expense	(171)		469		(392)		1,550		(66)		2,105
Net income (loss)	279	[1]	(1,065)	[1]	635	[1]	(2,604)	[1]	203	[1]	(3,601)	[1]
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net Realized Gain on Sale of Securities	824		199		3,791		287		4,057		474
Unrealized Losses on Available-for-Sale Securities included in Pre-Tax Income	0		0		0		0		0		(313)
Income (Loss) before income tax	824		199		3,791		287		4,057		161
Income tax expense	(133)		(41)		(699)		(45)		(771)		(10)
Net income (loss)	691		158		3,092		242		3,286		151
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest on long-term debt and revolving credit facility	(110)		(104)		(326)		(306)		(431)		(405)
Income (Loss) before income tax	(110)		(104)		(326)		(306)		(431)		(405)
Income tax expense	42		39		174		129		213		143
Net income (loss)	$ (68)		$ (65)		$ (152)		$ (177)		$ (218)		$ (262)

[1] These items are included in the computation of net periodic benefit cost. See Note I, Employee Benefits, for additional information.