Pension and Other Postretirement Benefits (details) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Mar. 31, 2013	Dec. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive loss	$ (8,594,000)		$ (7,301,000)		$ (8,594,000)		$ (7,301,000)		$ (8,826,000)	$ (9,291,000)
Total Amounts Reclassified Into Accumulated Other Comprehensive Income	0				0
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Benefit Cost, before Tax	(1,000)				(5,000)
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, before Tax	385,000				1,156,000
Other Comprehensive Income Total Reclassifications Before Tax	384,000				1,151,000
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Pension Cost, Tax	(152,000)		(108,000)		(454,000)		(325,000)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	232,000		167,000		697,000		499,000
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Qualified Defined Benefit Pension Plan Contributions					8,900,000
Qualified Contributions Expected During Next Fiscal Year					approximately $3 million
Multiemployer Plan, Period Contributions					300,000		200,000
Defined Contribution Plan, Cost Recognized					2,300,000		1,700,000
Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan, Service Cost	2,341,000		2,130,000		7,023,000		6,390,000
Defined Benefit Plan, Interest Cost	4,103,000		4,303,000		12,310,000		12,911,000
Defined Benefit Plan Expected Return On Plan Assets	(4,678,000)		(4,637,000)		(14,034,000)		(13,914,000)
Defined Benefit Plan Amortization Of Net Actuarial Loss	4,421,000		3,844,000		13,263,000		11,531,000
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	56,000		48,000		167,000		146,000
Defined Benefit Plan Amortization Of Transition Obligations	0		0		0		0
Defined Benefit Plan Net Periodic Benefit Cost	6,243,000		5,688,000		18,729,000		17,064,000
Defined Benefit Plan Amount Allocated To Construction	(1,910,000)		(1,676,000)		(5,566,000)		(4,522,000)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	(2,230,000)	[1]	(2,111,000)	[1]	(6,850,000)	[1]	(6,273,000)	[1]
Defined Benefit Plan Net Amount Charged To Expense	2,103,000		1,901,000		6,313,000		6,269,000
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan, Service Cost	178,000		177,000		536,000		531,000
Defined Benefit Plan, Interest Cost	286,000		314,000		858,000		943,000
Defined Benefit Plan Expected Return On Plan Assets	0		0		0		0
Defined Benefit Plan Amortization Of Net Actuarial Loss	169,000		103,000		507,000		309,000
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	50,000		50,000		148,000		148,000
Defined Benefit Plan Amortization Of Transition Obligations	0		103,000		0		309,000
Defined Benefit Plan Net Periodic Benefit Cost	683,000		747,000		2,049,000		2,240,000
Defined Benefit Plan Amount Allocated To Construction	(226,000)		(252,000)		(656,000)		(681,000)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	0	[1]	0	[1]	0	[1]	0	[1]
Defined Benefit Plan Net Amount Charged To Expense	$ 457,000		$ 495,000		$ 1,393,000		$ 1,559,000

[1] Effective January 1, 2011, the OPUC approved the deferral of certain pension expenses above or below the amount set in rates, with recovery of these deferred amounts through the implementation of a balancing account, which includes the expectation of lower net periodic benefit costs in future years. Deferred pension expense balances earn a carrying charge