Pension and Other Postretirement Benefits (details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
General Discussion Of Pension And Other Postretirement Benefits Abstract
Qualified Defined Benefit Pension Plan Contributions			$ 18,400,000
Defined Benefit Plan Estimated Future Employer Contributions In Current Fiscal Year Range			up to $10 million
Multiemployer Plan Contributions			200,000	200,000
Defined Contribution Plan, Cost Recognized			1,200,000	1,300,000
Pension Plans Defined Benefit [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan Service Cost	2,130,000	1,900,000	4,260,000	3,799,000
Defined Benefit Plan Interest Cost	4,304,000	4,526,000	8,608,000	9,053,000
Defined Benefit Plan Expected Return On Plan Assets	(4,639,000)	(4,456,000)	(9,277,000)	(8,912,000)
Defined Benefit Plan Amortization Of Net Actuarial Loss	3,844,000	2,692,000	7,687,000	5,384,000
Defined Benefit Plan Amortization Of Prior Service Costs	49,000	88,000	98,000	176,000
Defined Benefit Plan Amortization Of Transition Obligations	0	0	0	0
Defined Benefit Plan Net Periodic Benefit Cost	5,688,000	4,750,000	11,376,000	9,500,000
Defined Benefit Plan Amount Allocated To Construction	(1,428,000)	(1,251,000)	(2,846,000)	(2,486,000)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	(2,094,000)	(1,329,000)	(4,162,000)	(2,659,000)
Defined Benefit Plan Net Amount Charged To Expense	2,166,000	2,170,000	4,368,000	4,355,000
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	354,000	336,000
Defined Benefit Plan Interest Cost	315,000	343,000	629,000	687,000
Defined Benefit Plan Expected Return On Plan Assets	0	0	0	0
Defined Benefit Plan Amortization Of Net Actuarial Loss	103,000	68,000	206,000	136,000
Defined Benefit Plan Amortization Of Prior Service Costs	49,000	49,000	98,000	98,000
Defined Benefit Plan Amortization Of Transition Obligations	103,000	103,000	206,000	206,000
Defined Benefit Plan Net Periodic Benefit Cost	747,000	731,000	1,493,000	1,463,000
Defined Benefit Plan Amount Allocated To Construction	(215,000)	(229,000)	(429,000)	(455,000)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	0	0	0	0
Defined Benefit Plan Net Amount Charged To Expense	$ 532,000	$ 502,000	$ 1,064,000	$ 1,008,000