Accumulated Other Comprehensive Income (Loss) (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net unrealized gains (losses) on marketable securities, beginning of period	$ 13,663	$ 11,298	$ 5,868
Other comprehensive income (loss), net unrealized gains (losses) on marketable securities	10,969	2,928	6,787
Income tax beneift (expense), net unrealized gains (losses) on marketable securities	(2,438)	(563)	(1,357)
Net unrealized gains (losses) on marketable securities, end of period	22,194	13,663	11,298
Unrecognized pension and postretirement benefit cost, beginning of period	(78,373)	(31,522)	(42,586)
Other comprehensive income (loss), unrecognized pension and postretirement benefit costs	4,100	(76,985)	17,351
Income tax benefit (expense), unrecognized pension and postretirement benefit costs, tax	(1,464)	30,134	(6,287)
Unrecognized pension and postretirement benefit cost, end of period	(75,737)	(78,373)	(31,522)
Net losses on cash flow hedges, beginning of period	(12,795)	(12,953)	(13,169)
Other comprehensive income (loss), net losses on cash flow hedges	385	361	338
Income tax benefit (expense), net losses on cash flow hedges	(131)	(203)	(122)
Net losses on cash flow hedges, end of period	(12,541)	(12,795)	(12,953)
Accumulated other comprehensive income (loss), net of tax, beginning of period	(77,505)	(33,177)	(49,887)
Total other comprehensive income (loss) before income taxes	15,454	(73,696)	24,476
Total income tax benefit (expense)	(4,033)	29,368	(7,766)
Accumulated other comprehensive income (loss), net of tax, end of period	$ (66,084)	$ (77,505)	$ (33,177)