Pension and Other Postretirement Benefits (details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 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	$ (8,826,000)		$ (7,467,000)		$ (8,826,000)		$ (7,467,000)		$ (9,058,000)	$ (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	(2,000)				(4,000)
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, before Tax	385,000				771,000
Other Comprehensive Income Total Reclassifications Before Tax	383,000				767,000
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Pension Cost, Tax	(151,000)		(109,000)		(302,000)		(217,000)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	232,000		166,000		465,000		332,000
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Qualified Defined Benefit Pension Plan Contributions					4,200,000
Qualified Contributions Expected During Next Fiscal Year					approximately $8 million
Multiemployer Plan, Period Contributions					200,000		200,000
Defined Contribution Plan, Cost Recognized					1,600,000		1,200,000
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		4,682,000		4,260,000
Defined Benefit Plan, Interest Cost	4,104,000		4,304,000		8,207,000		8,608,000
Defined Benefit Plan Expected Return On Plan Assets	(4,678,000)		(4,639,000)		(9,356,000)		(9,277,000)
Defined Benefit Plan Amortization Of Net Actuarial Loss	4,421,000		3,844,000		8,842,000		7,687,000
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	55,000		49,000		111,000		98,000
Defined Benefit Plan Amortization Of Transition Obligations	0		0		0		0
Defined Benefit Plan Net Periodic Benefit Cost	6,243,000		5,688,000		12,486,000		11,376,000
Defined Benefit Plan Amount Allocated To Construction	(1,801,000)		(1,428,000)		(3,656,000)		(2,846,000)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	(2,271,000)	[1]	(2,094,000)	[1]	(4,620,000)	[1]	(4,162,000)	[1]
Defined Benefit Plan Net Amount Charged To Expense	2,171,000		2,166,000		4,210,000		4,368,000
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan, Service Cost	179,000		177,000		358,000		354,000
Defined Benefit Plan, Interest Cost	286,000		315,000		572,000		629,000
Defined Benefit Plan Expected Return On Plan Assets	0		0		0		0
Defined Benefit Plan Amortization Of Net Actuarial Loss	169,000		103,000		338,000		206,000
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	49,000		49,000		98,000		98,000
Defined Benefit Plan Amortization Of Transition Obligations	0		103,000		0		206,000
Defined Benefit Plan Net Periodic Benefit Cost	683,000		747,000		1,366,000		1,493,000
Defined Benefit Plan Amount Allocated To Construction	(211,000)		(215,000)		(430,000)		(429,000)
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	$ 472,000		$ 532,000		$ 936,000		$ 1,064,000

[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 accrue interest at the utility’s actual cost of long-term debt. See Note 2.