STATEMENTS OF COMPREHENSIVE OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net income	$ 96,768	$ 81,918	$ 91,428
Unrecognized pension and post-retirement benefit costs:
Net gain (loss) arising during period	(20,053)	5,429	(54,328)
Prior service benefit	32,697	824	34,200
Reclassification adjustments included in net income for amortization of:
Prior service benefit	(7,407)	(6,574)	(7,659)
Net loss	4,965	8,622	6,182
Net unrealized gains/losses on marketable securities:
Net holding gains (losses) arising during period	8,444	(2,906)	10,827
Reclassification adjustments for net gains included in net income	(7,640)	(11,114)	(7,350)
Net losses on cash flow hedges:
Reclassification adjustment for interest expense included in net income	498	467	438
Total other comprehensive income (loss) before income taxes	11,504	(5,252)	(17,690)
Income tax benefit (expense) related to items of other comprehensive income (loss):
Unrecognized pension and post-retirement benefit costs	(4,261)	(3,286)	8,051
Net unrealized (gains) losses on marketable securities	(106)	2,828	(760)
Losses on cash flow hedges	(339)	(203)	(214)
Total income tax benefit (expense)	(4,706)	(661)	7,077
Other comprehensive income (loss), net of tax	6,798	(5,913)	(10,613)
Comprehensive income	$ 103,566	$ 76,005	$ 80,815