Pension and Other Postretirement Benefits (details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
General Discussion Of Pension And Other Postretirement Benefits Abstract
Western States Pension Contributions			$ 200,000	$ 200,000
Qualified Defined Benefit Pension Plan Contributions			16,400,000
Defined Benefit Plan Estimated Future Employer Contributions In Current Fiscal Year Range			between $5 million and $7 million
Pension Plans Defined Benefit [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan Service Cost	1,900,000	1,773,000	3,799,000	3,546,000
Defined Benefit Plan Interest Cost	4,526,000	4,492,000	9,053,000	8,983,000
Defined Benefit Plan Expected Return On Plan Assets	(4,456,000)	(4,563,000)	(8,912,000)	(9,127,000)
Defined Benefit Plan Amortization Of Net Actuarial Loss	2,692,000	1,768,000	5,384,000	3,536,000
Defined Benefit Plan Amortization Of Prior Service Costs	88,000	204,000	176,000	410,000
Defined Benefit Plan Amortization Of Transition Obligations	0	0	0	0
Defined Benefit Plan Net Periodic Benefit Cost	4,750,000	3,674,000	9,500,000	7,348,000
Defined Benefit Plan Amount Allocated To Construction	(1,251,000)	(947,000)	(2,486,000)	(1,900,000)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	(1,329,000)	0	(2,659,000)	0
Defined Benefit Plan Net Amount Charged To Expense	2,170,000	2,727,000	4,355,000	5,448,000
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	336,000	312,000
Defined Benefit Plan Interest Cost	343,000	342,000	687,000	685,000
Defined Benefit Plan Expected Return On Plan Assets	0	0	0	0
Defined Benefit Plan Amortization Of Net Actuarial Loss	68,000	8,000	136,000	15,000
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	731,000	658,000	1,463,000	1,316,000
Defined Benefit Plan Amount Allocated To Construction	(229,000)	(207,000)	(455,000)	(415,000)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	0	0	0	0
Defined Benefit Plan Net Amount Charged To Expense	$ 502,000	$ 451,000	$ 1,008,000	$ 901,000