Accumulated Other Comprehensive Income Amounts Reclassified (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			12 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Mar. 31, 2013		Mar. 31, 2012
Marketable Securities:
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, before Tax	$ (158)			$ (934)
Unrealized Losses on Available-for-Sales Recognized in Earnings, before Tax	0			(479)
Reclassification adjustments for net (gains) losses included in net income	(158)		213	(1,413)		(1,350)
Tax effect on gain and loss from available-for-sale securities	37			299
Other Comprehensive Income (Loss), Reclassification Adjustment for Available-For-Sale Securities Included in Net Income, Net of Tax	(121)			(1,114)
Amortization of Pension and Postretirement Benefit Costs:
Prior service benefit	1,400	[1]	1,443	5,719	[1]	5,800
Net loss	(2,675)	[1]	(3,125)	(11,521)	[1]	(8,155)
Amortization of Prior Service Benefit and Net loss, before tax	(1,275)			(5,802)
Tax effect of the amortization of pension and postretirement benefit costs	570			2,324
Other comprehensive income loss reclassification adjustment pension and other postretirement benefit plans, net of tax	(705)			(3,478)
Cash Flow Hedge Gain (Loss) Reclassified to Earnings:
Cash Flow Hedge Loss Reclassified to Interest Expense	(101)			(392)
Reclassification adjustment for interest expense included in net income	(101)		(94)	(392)		(367)
Income tax expense on losses on cash flow hedges	52		45	138		215
Other Comprehensive Income (Loss), Reclassification Adjustment for Loss on Cash Flow Hedge Included in Net Income, Net of Tax	(49)			(254)
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ (875)			$ (4,846)

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