Accumulated Other Comprehensive Income Amounts Reclassified (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2014		Mar. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Prior service benefit	$ 1,459		$ 1,400		$ 5,619		$ 5,719
Unrealized Losses on Available-for-Sale Securities included in Pre-Tax Income	0		0		0		479
Interest on long-term debt and revolving credit facility	(11,822)		(11,820)		(47,714)		(45,516)
Income tax expense	1,473		3,315		41,813		49,517
Net income (loss)	4,579		7,608		85,304		94,888
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net income (loss)	2,499		(875)		612		(4,846)
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Prior service benefit	1,459	[1]	1,400	[1]	5,619	[1]	5,719	[1]
Net Loss	(1,123)	[1]	(2,675)	[1]	(8,920)	[1]	(11,521)	[1]
Income (Loss) before income tax	336	[1]	(1,275)	[1]	(3,301)	[1]	(5,802)	[1]
Income tax expense	(131)		570		1,256		2,324
Net income (loss)	205	[1]	(705)	[1]	(2,045)	[1]	(3,478)	[1]
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net Realized Gain (Loss) on Sale of Securities	2,865		(158)		3,576		(934)
Unrealized Losses on Available-for-Sale Securities included in Pre-Tax Income	0		0		0		(479)
Income (Loss) before income tax	2,865		(158)		3,576		(1,413)
Income tax expense	(556)		37		(710)		299
Net income (loss)	2,309		(121)		2,866		(1,114)
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	(107)		(101)		(417)		(392)
Income (Loss) before income tax	(107)		(101)		(417)		(392)
Income tax expense	92		52		208		138
Net income (loss)	$ (15)		$ (49)		$ (209)		$ (254)

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