Accumulated Other Comprehensive Income Amounts Reclassified (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income (Loss) before income tax		$ (8,969)	$ 4,442	$ 103,402	$ 130,870
Income tax expense		3,161	(984)	(30,750)	(40,599)
Net (Income) Loss		(5,808)	3,458	72,652	90,271
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]	1,666	1,663	6,577	7,863
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]	(1,223)	(2,250)	(7,595)	(7,309)
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]	443	(587)	(1,018)	554
Reclassification from AOCI, Current Period, Tax		(56)	331	423	(89)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	387	(256)	(595)	465
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		1,113	2,997	7,053	6,665
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(40)	(42)	(262)	(251)
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(1,460)	(2,699)	(6,196)	(6,879)
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		1,388	3,745	8,757	8,230
Income (Loss) before income tax		1,388	3,745	8,757	8,230
Income tax expense		(275)	(748)	(1,704)	(1,565)
Net (Income) Loss		1,113	2,997	7,053	6,665
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]
Income (Loss) before income tax		(122)	(114)	(475)	(445)
Income tax expense		82	72	213	194
Net (Income) Loss		(40)	(42)	(262)	(251)
Interest Rate Contract | 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		$ (122)	$ (114)	$ (475)	$ (445)

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