Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Employee benefits	$ 231,386	$ 248,481
Self-insurance accruals	32,336	37,426
Capital-loss carryforwards		695
Operating-loss carryforwards	49,125	57,635
Tax-credit carryforwards	9,138	6,877
Share-based compensation	15,558	13,724
Other	13,242	14,350
Increased valuation allowance	(19,120)	(17,515)
Total deferred income tax assets	331,665	361,673
Property, plant and equipment	331,325	313,041
Prepaid expenses	27,626	25,056
Revenue	6,808	6,939
Other	8,798	8,269
Total deferred income tax liabilities	374,557	353,305
Net deferred tax asset (liability)	$ (42,892)	$ 8,368