Statements Of Comprehensive Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Net income	$ 56,740	$ 52,476	$ 81,270	$ 87,187	$ 85,511	$ 88,378
Unrecognized pension and post-retirement benefit costs:
Net gain (loss) arising during period	0	0	0	19,700	(74,028)	102,664
Prior service benefit	0	0	0	0	34,200	97
Reclassification adjustments included in net income for amortization of:
Prior service benefit	(1,606)	(2,065)	(4,931)	(5,594)	(6,996)	(6,985)
Net loss	1,966	1,615	6,466	4,567	8,081	6,716
Net unrealized gains/losses on marketable securities:
Net holding gains (losses) arising during period	(8,092)	897	(8,641)	7,965	(5,779)	16,803
Reclassification adjustments for net gains included in net income	(4,324)	(824)	(7,887)	(3,791)	(11,446)	(4,057)
Net losses on cash flow hedges:
Reclassification adjustment for interest expense included in net income	118	110	348	326	460	431
Total other comprehensive income (loss) before income taxes	(11,938)	(267)	(14,645)	23,173	(55,508)	115,669
Income tax benefit (expense) related to items of other comprehensive income (loss):
Unrecognized pension and post-retirement benefit costs	(134)	171	(756)	(7,161)	14,456	(39,177)
Net unrealized losses (gains) on marketable securities	2,459	(31)	3,340	(889)	3,469	(2,556)
Losses on cash flow hedges	(46)	(42)	(161)	(174)	(201)	(213)
Total income tax benefit (expense)	2,279	98	2,423	(8,224)	17,724	(41,946)
Other comprehensive income (loss), net of tax	(9,659)	(169)	(12,222)	14,949	(37,784)	73,723
Comprehensive income	$ 47,081	$ 52,307	$ 69,048	$ 102,136	$ 47,727	$ 162,101