Statements Of Comprehensive Operations - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Net income (loss)	$ (3,989)	$ (5,808)	$ 98,587	$ 72,652
Unrecognized pension and post-retirement benefit costs:
Net gain (loss) arising during period	0	0	(20,053)	5,429
Prior service benefit	0	0	32,697	824
Reclassification adjustments included in net income for amortization of:
Prior service benefit	(2,416)	(1,666)	(8,157)	(6,577)
Net loss	1,694	1,223	5,436	7,595
Net unrealized gains/losses on marketable securities:
Net holding gains (losses) arising during period	7,721	2,190	13,975	(1,730)
Reclassification adjustments for net gains included in net income	(2,191)	(1,388)	(8,443)	(8,757)
Net losses on cash flow hedges:
Reclassification adjustment for interest expense included in net income	130	122	506	475
Total other comprehensive income (loss) before income taxes	4,938	481	15,961	(2,741)
Income tax benefit (expense) related to items of other comprehensive income (loss):
Unrecognized pension and post-retirement benefit costs	193	56	(4,124)	(2,899)
Net unrealized (gains) losses on marketable securities	(1,121)	(173)	(1,054)	2,099
Losses on cash flow hedges	(78)	(82)	(335)	(213)
Total income tax expense	(1,006)	(199)	(5,513)	(1,013)
Other comprehensive income (loss), net of tax	3,932	282	10,448	(3,754)
Comprehensive income (loss)	$ (57)	$ (5,526)	$ 109,035	$ 68,898