Statements Of Comprehensive Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Net income	$ 74,636	$ 56,740	$ 91,112	$ 81,270	$ 91,760	$ 85,511
Unrecognized pension and post-retirement benefit costs:
Net gain (loss) arising during period	0	0	0	0	5,429	(74,028)
Prior service benefit	0	0	0	0	824	34,200
Reclassification adjustments included in net income for amortization of:
Prior service benefit	(1,663)	(1,606)	(4,993)	(4,931)	(6,636)	(6,996)
Net loss	1,087	1,966	3,532	6,466	5,688	8,081
Net unrealized gains/losses on marketable securities:
Net holding gains (losses) arising during period	4,313	(8,092)	9,293	(8,641)	15,028	(5,779)
Reclassification adjustments for net gains included in net income	(2,072)	(4,324)	(5,570)	(7,887)	(8,797)	(11,446)
Net losses on cash flow hedges:
Reclassification adjustment for interest expense included in net income	126	118	371	348	490	460
Total other comprehensive income (loss) before income taxes	1,791	(11,938)	2,633	(14,645)	12,026	(55,508)
Income tax benefit (expense) related to items of other comprehensive income (loss):
Unrecognized pension and post-retirement benefit costs	(228)	(134)	(6)	(756)	(2,536)	14,456
Net unrealized losses (gains) on marketable securities	(435)	2,459	(757)	3,340	(1,269)	3,469
Losses on cash flow hedges	(165)	(46)	(293)	(161)	(335)	(201)
Total income tax benefit (expense)	(828)	2,279	(1,056)	2,423	(4,140)	17,724
Other comprehensive income (loss), net of tax	963	(9,659)	1,577	(12,222)	7,886	(37,784)
Comprehensive income	$ 75,599	$ 47,081	$ 92,689	$ 69,048	$ 99,646	$ 47,727