Pension and Other Postretirement Benefits (details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
General Discussion Of Pension And Other Postretirement Benefits Abstract
Multiemployer Plan Contributions	$ 100,000
Defined Contribution Plan, Cost Recognized	700,000	800,000
Qualified Defined Benefit Pension Plan Contributions	13,800,000
Defined Benefit Plan Estimated Future Employer Contributions In Current Fiscal Year Range	approximately $14 million
Pension Plans Defined Benefit [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan Service Cost	2,130,000	1,899,000
Defined Benefit Plan Interest Cost	4,304,000	4,527,000
Defined Benefit Plan Expected Return On Plan Assets	(4,638,000)	(4,456,000)
Defined Benefit Plan Amortization Of Net Actuarial Loss	3,843,000	2,692,000
Defined Benefit Plan Amortization Of Prior Service Costs	49,000	88,000
Defined Benefit Plan Amortization Of Transition Obligations	0	0
Defined Benefit Plan Net Periodic Benefit Cost	5,688,000	4,750,000
Defined Benefit Plan Amount Allocated To Construction	(1,418,000)	(1,235,000)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	(2,068,000)	(1,330,000)
Defined Benefit Plan Net Amount Charged To Expense	2,202,000	2,185,000
Other Postretirement Benefit Plans Defined Benefit [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan Service Cost	177,000	168,000
Defined Benefit Plan Interest Cost	314,000	344,000
Defined Benefit Plan Expected Return On Plan Assets	0	0
Defined Benefit Plan Amortization Of Net Actuarial Loss	103,000	68,000
Defined Benefit Plan Amortization Of Prior Service Costs	49,000	49,000
Defined Benefit Plan Amortization Of Transition Obligations	103,000	103,000
Defined Benefit Plan Net Periodic Benefit Cost	746,000	732,000
Defined Benefit Plan Amount Allocated To Construction	(214,000)	(226,000)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	0	0
Defined Benefit Plan Net Amount Charged To Expense	$ 532,000	$ 506,000