Taxes on Income (Schedule Of Deferred Tax Assets And Liabilities) (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Current deferred tax assets [Abstract]
Compensated absences	$ 750,000	$ 695,000
Allowance for doubtful accounts	1,652,000	1,752,000
Insurance accruals	3,306,000	4,150,000
Other	6,588,000	7,589,000
Current deferred tax assets, Total	12,296,000	14,186,000
Deferred tax assets [Abstract]
Postretirement health care benefits	3,215,000	3,422,000
Insurance accruals	1,556,000	1,420,000
Deferred compensation	8,449,000	8,290,000
Unrealized loss on derivative financial instruments	563,000	3,384,000
Unrealized loss on defined benefit plans	33,942,000	28,114,000
Operating loss carryforwards	601,000	1,305,000
Other	13,443,000	9,047,000
Deferred tax assets	61,769,000	54,982,000
Deferred tax liabilities [Abstract]
Property	(408,905,000)	(298,335,000)
Deferred state taxes	(39,072,000)	(25,738,000)
Pension benefits	(18,794,000)	(15,376,000)
Goodwill and other intangibles	(20,220,000)	(6,563,000)
Other	(874,000)	(1,325,000)
Deferred tax liabilities	(487,865,000)	(347,337,000)
Deferred tax assets (liabilities)	$ (426,096,000)	$ (292,355,000)