Accumulated Other Comprehensive Income Amounts Reclassified (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income (loss) before income taxes		$ (6,277)	$ (8,969)	$ 153,378	$ 103,402
Income tax expense (benefit)		2,288	3,161	(54,791)	(30,750)
Net (Income) Loss		(3,989)	(5,808)	98,587	72,652
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]	2,416	1,666	8,157	6,577
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]	(1,694)	(1,223)	(5,436)	(7,595)
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]	722	443	2,721	(1,018)
Reclassification from AOCI, Current Period, Tax		(193)	(56)	(1,157)	423
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	529	387	1,564	(595)
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		1,756	1,113	6,849	7,053
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		(52)	(40)	(171)	(262)
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		(2,233)	(1,460)	(8,242)	(6,196)
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		2,191	1,388	8,443	8,757
Income (loss) before income taxes		2,191	1,388	8,443	8,757
Income tax expense (benefit)		(435)	(275)	(1,594)	(1,704)
Net (Income) Loss		1,756	1,113	6,849	7,053
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 taxes		(130)	(122)	(506)	(475)
Income tax expense (benefit)		78	82	335	213
Net (Income) Loss		(52)	(40)	(171)	(262)
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		$ (130)	$ (122)	$ (506)	$ (475)

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