Pension and Other Postretirement Benefits (details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
General Discussion Of Pension And Other Postretirement Benefits Abstract
Multiemployer Plan Contributions			$ 300,000	$ 300,000
Qualified Defined Benefit Pension Plan Contributions			19,200,000
Defined Benefit Plan Estimated Future Employer Contributions In Current Fiscal Year Range			up to $4 million
Pension Plans Defined Benefit [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan Service Cost	1,839,000	1,435,000	5,638,000	4,981,000
Defined Benefit Plan Interest Cost	4,503,000	4,517,000	13,556,000	13,500,000
Defined Benefit Plan Expected Return On Plan Assets	(4,455,000)	(4,528,000)	(13,367,000)	(13,655,000)
Defined Benefit Plan Amortization Of Net Actuarial Loss	2,683,000	2,028,000	8,067,000	5,564,000
Defined Benefit Plan Amortization Of Prior Service Costs	88,000	(270,000)	264,000	140,000
Defined Benefit Plan Amortization Of Transition Obligations	0	0	0	0
Defined Benefit Plan Net Periodic Benefit Cost	4,658,000	3,182,000	14,158,000	10,530,000
Defined Benefit Plan Amount Allocated To Construction	(1,279,000)	(897,000)	(3,765,000)	(2,797,000)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	(1,330,000)	0	(3,989,000)	0
Defined Benefit Plan Net Amount Charged To Expense	2,049,000	2,285,000	6,404,000	7,733,000
Other Postretirement Benefit Plans Defined Benefit [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan Service Cost	168,000	156,000	504,000	468,000
Defined Benefit Plan Interest Cost	344,000	343,000	1,031,000	1,028,000
Defined Benefit Plan Expected Return On Plan Assets	0	0	0	0
Defined Benefit Plan Amortization Of Net Actuarial Loss	68,000	7,000	204,000	22,000
Defined Benefit Plan Amortization Of Prior Service Costs	50,000	50,000	148,000	148,000
Defined Benefit Plan Amortization Of Transition Obligations	103,000	103,000	309,000	309,000
Defined Benefit Plan Net Periodic Benefit Cost	733,000	659,000	2,196,000	1,975,000
Defined Benefit Plan Amount Allocated To Construction	(234,000)	(231,000)	(689,000)	(646,000)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	0	0	0	0
Defined Benefit Plan Net Amount Charged To Expense	$ 499,000	$ 428,000	$ 1,507,000	$ 1,329,000