STATEMENTS OF COMPREHENSIVE OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net income	$ 123,037	$ 84,315	$ 98,261
Unrecognized pension and post-retirement benefit costs:
Net gain (loss) arising during period	(12,110)	(5,898)	12,634
Reclassification adjustments included in net income for amortization of:
Prior service benefit	(8,740)	(9,657)	(9,657)
Net loss	3,415	6,387	6,776
Net unrealized gains/losses on marketable securities:
Net holding gains (losses) arising during period	6,072	(4,072)	25,275
Reclassification adjustments for net (gains) losses included in net income	(2,232)	1,445	(10,626)
Net losses on cash flow hedges:
Reclassification adjustment for interest expense included in net income	605	568	532
Total other comprehensive income (loss) before income taxes	(12,990)	(11,227)	24,934
Income tax benefit (expense) related to items of other comprehensive income (loss):
Unrecognized pension and post-retirement benefit costs	3,867	2,035	(3,615)
Net unrealized (gains) losses on marketable securities	(898)	523	(2,922)
Losses on cash flow hedges	(147)	(145)	(223)
Total income tax benefit (expense)	2,822	2,413	(6,760)
Other comprehensive income (loss), net of tax	(10,168)	(8,814)	18,174
Comprehensive income	$ 112,869	$ 75,501	$ 116,435