CONSOLIDATED STATEMENTS OF COMPREHENSIVE OPERATIONS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net income	$ 90,846	$ 103,539	$ 100,603
Unrecognized pension and postretirement benefit costs:
Net loss arising during period	(2,109)	(77,678)	(9,874)
Prior service benefit	0	0	26,605
Reclassification adjustments included in net income for amortization of:
Prior service cost	(5,762)	(5,812)	(2,754)
Net loss	11,971	6,505	3,374
Net unrealized gains on marketable securities:
Net holding gains arising during period	9,927	1,570	6,665
Reclassification adjustments for net losses included in net income	1,042	1,358	122
Net losses on cash flow hedges:
Reclassification adjustment for interest expense included in net income	385	361	338
Total other comprehensive income (loss) before income taxes	15,454	(73,696)	24,476
Income tax benefit (expense) related to items of other comprehensive income (loss):
Unrecognized pension and postretirement benefit costs	(1,464)	30,134	(6,287)
Net unrealized gains on marketable securities	(2,438)	(563)	(1,357)
Losses on cash flow hedges	(131)	(203)	(122)
Total income tax benefit (expense)	(4,033)	29,368	(7,766)
Other comprehensive income (loss), net of tax	11,421	(44,328)	16,710
Comprehensive income	$ 102,267	$ 59,211	$ 117,313