Consolidated Statements Of Comprehensive Operations (USD $) In Thousands, unless otherwise specified	3 Months Ended			12 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Mar. 31, 2013		Mar. 31, 2012
Net income	$ 7,634		$ 3,344	$ 95,136		$ 100,108
Unrecognized pension and postretirement benefit costs:
Net loss arising during period	0		0	(2,109)		(77,678)
Reclassification adjustments included in net income for amortization of:
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
Net unrealized gains (losses) on marketable securities:
Net holding gains arising during period	6,793		8,158	8,562		7,555
Reclassification adjustments for net (gains) losses included in net income	158		(213)	1,413		1,350
Net losses on cash flow hedges:
Reclassification adjustment for interest expense included in net income	101		94	392		367
Total other comprehensive income (loss) before income taxes	8,327		9,721	14,060		(66,051)
Income tax benefit (expense) related to items of other comprehensive income (loss):
Unrecognized pension and postretirement benefit costs	(570)		(555)	(1,479)		29,586
Net unrealized gains on marketable securities	(1,287)		(1,559)	(2,166)		(1,762)
Losses on cash flow hedges	(52)		(45)	(138)		(215)
Total income tax benefit (expense)	(1,909)		(2,159)	(3,783)		27,609
Other comprehensive income (loss), net of tax	6,418		7,562	10,277		(38,442)
Comprehensive income	$ 14,052		$ 10,906	$ 105,413		$ 61,666

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