Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Abstract]
Employee benefits	$ 248,481	$ 163,119
Self-insurance accruals	37,426	42,950
Capital-loss carryforwards	695	92
Operating-loss carryforwards	57,635	15,636
Tax-credit carryforwards	6,877	6,259
Share-based compensation	13,724	12,650
Other	14,350	14,161
Valuation allowance	(17,515)	(12,749)
Total deferred income tax assets	361,673	242,118
Property, plant and equipment	313,041	245,083
Prepaid expenses	25,056	23,814
Revenue	6,939	7,562
Other	8,269	5,658
Total deferred income tax liabilities	353,305	282,117
Net deferred tax asset (liability)	$ 8,368	$ (39,999)