Accumulated Other Comprehensive Income (Loss) (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net unrealized gains (losses) on marketable securities, beginning of period	$ 11,298	$ 5,868	$ (6,159)
Other comprehensive income (loss), net unrealized gains (losses) on marketable securities	2,928	6,787	15,034
Income tax beneift (expense), net unrealized gains (losses) on marketable securities	(563)	(1,357)	(3,007)
Net unrealized gains (losses) on marketable securities, end of period	13,663	11,298	5,868
Unrecognized pension and postretirement benefit cost, beginning of period	(31,522)	(42,586)	(9,834)
Other comprehensive income (loss), unrecognized pension and postretirement benefit costs	(76,985)	17,351	(49,709)
Income tax benefit (expense), unrecognized pension and postretirement benefit costs, tax	30,134	(6,287)	16,957
Unrecognized pension and postretirement benefit cost, end of period	(78,373)	(31,522)	(42,586)
Net losses on cash flow hedges, beginning of period	(12,953)	(13,169)	(13,371)
Other comprehensive income (loss), net losses on cash flow hedges	361	338	317
Income rax benefit (expense), net losses on cash flow hedges	(203)	(122)	(115)
Net losses on cash flow hedges, end of period	(12,795)	(12,953)	(13,169)
Accumulated other comprehensive income (loss), net of tax, beginning of period	(33,177)	(49,887)	(29,364)
Total other comprehensive income (loss), accumulated other comprehensive loss	(73,696)	24,476	(34,358)
Total income tax benefit (expense)	29,368	(7,766)	13,835
Accumulated other comprehensive income (loss), net of tax, end of period	$ (77,505)	$ (33,177)	$ (49,887)