Statements Of Comprehensive Operations - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Net income (loss)	$ (5,808)	$ 3,458	$ 72,652	$ 90,271
Unrecognized pension and post-retirement benefit costs:
Net gain (loss) arising during period	0	0	5,429	(74,028)
Prior service benefit	0	0	824	34,200
Reclassification adjustments included in net income for amortization of:
Prior service benefit	(1,666)	(1,663)	(6,577)	(7,863)
Net loss	1,223	2,250	7,595	7,309
Net unrealized gains/losses on marketable securities:
Net holding gains (losses) arising during period	2,190	1,014	(1,730)	10,843
Reclassification adjustments for net gains included in net income	(1,388)	(3,745)	(8,757)	(8,230)
Net losses on cash flow hedges:
Reclassification adjustment for interest expense included in net income	122	114	475	445
Total other comprehensive income (loss) before income taxes	481	(2,030)	(2,741)	(37,324)
Income tax benefit (expense) related to items of other comprehensive income (loss):
Unrecognized pension and post-retirement benefit costs	56	(331)	(2,899)	15,142
Net unrealized losses (gains) on marketable securities	(173)	556	2,099	(561)
Losses on cash flow hedges	(82)	(72)	(213)	(194)
Total income tax benefit (expense)	(199)	153	(1,013)	14,387
Other comprehensive income (loss), net of tax	282	(1,877)	(3,754)	(22,937)
Comprehensive income (loss)	$ (5,526)	$ 1,581	$ 68,898	$ 67,334