Pension and Other Postretirement Benefits (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive loss	$ (9,744)		$ (6,193)		$ (10,076)	$ (6,358)
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Benefit Cost, before Tax	0		(2)
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, before Tax	548		276
Other Comprehensive Income Total Reclassifications Before Tax	548		274
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Pension Cost, Tax	(216)		(109)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	332		165
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Qualified Defined Benefit Pension Plan Contributions	2,630
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year	12,300
Defined Contribution Plan, Cost Recognized	1,100		500
Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan, Service Cost	2,308		1,918
Defined Benefit Plan, Interest Cost	4,596		4,512
Defined Benefit Plan Expected Return On Plan Assets	(5,174)		(4,886)
Defined Benefit Plan Amortization Of Net Actuarial Loss	4,561		2,580
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	58		56
Defined Benefit Plan Net Periodic Benefit Cost	6,349		4,180
Defined Benefit Plan Amount Allocated To Construction	(1,825)		(1,201)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	(2,175)	[1]	(1,101)	[1]
Defined Benefit Plan Net Amount Charged To Expense	2,349		1,878
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan, Service Cost	145		136
Defined Benefit Plan, Interest Cost	291		309
Defined Benefit Plan Expected Return On Plan Assets	0		0
Defined Benefit Plan Amortization Of Net Actuarial Loss	126		46
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	49		49
Defined Benefit Plan Net Periodic Benefit Cost	611		540
Defined Benefit Plan Amount Allocated To Construction	(191)		(171)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	0	[1]	0	[1]
Defined Benefit Plan Net Amount Charged To Expense	$ 420		$ 369

[1] The deferral of certain pension expenses above or below the amount set in rates was approved by the OPUC, 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 include accrued interest at the utility’s authorized rate of return, with the equity portion of the interest being unrecognized until amounts are collected in rates.