REGULATORY MATTERS: Level 4 (Details) (USD $)	6 Months Ended						12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Dec. 30, 2011 Idaho General Rate Case Settlement	Jun. 30, 2012 Settlement Stipulation -- Investment Tax Credit and Idaho Sharing Mechanism	Dec. 27, 2011 Settlement Stipulation -- Investment Tax Credit and Idaho Sharing Mechanism	Jan. 13, 2010 Settlement Stipulation -- Investment Tax Credit and Idaho Sharing Mechanism	Dec. 31, 2011 Revenue-Sharing Order Under January 2010 and December 2011 Settlement Agreements	Jun. 01, 2012 Annual Power Cost Adjustment Mechanism Filing	Jun. 01, 2011 Annual Power Cost Adjustment Mechanism Filing	Jun. 30, 2012 Idaho Fixed Cost Adjustment	Jun. 01, 2012 Idaho Fixed Cost Adjustment	Mar. 30, 2012 Idaho Fixed Cost Adjustment	Jul. 01, 2012 Langley Gulch Power Plant Cost Recovery Filing - Idaho	Jun. 29, 2012 Langley Gulch Power Plant Cost Recovery Filing - Idaho	Mar. 02, 2012 Langley Gulch Power Plant Cost Recovery Filing - Idaho	Jan. 02, 2012 Langley Gulch Power Plant Cost Recovery Filing - Idaho	Dec. 31, 2011 Langley Gulch Power Plant Cost Recovery Filing - Idaho	Sep. 01, 2009 Langley Gulch Power Plant Cost Recovery Filing - Idaho	Jun. 30, 2012 Energy Efficiency and Demand Response Programs	Mar. 15, 2012 Energy Efficiency and Demand Response Programs	Dec. 31, 2011 Energy Efficiency and Demand Response Programs	Aug. 18, 2011 Energy Efficiency and Demand Response Programs	Jun. 30, 2012 Cost Recovery for Cessation of Boardman Coal-Fired Operations	May 17, 2012 Cost Recovery for Cessation of Boardman Coal-Fired Operations	Feb. 15, 2012 Cost Recovery for Cessation of Boardman Coal-Fired Operations	Jun. 30, 2012 Idaho Depreciation Rate Filings	Jun. 01, 2012 Idaho Depreciation Rate Filings	Apr. 27, 2012 Idaho Depreciation Rate Filings	Feb. 15, 2012 Idaho Depreciation Rate Filings	Mar. 01, 2012 Oregon General Rate Case Filing	Jul. 29, 2011 Oregon General Rate Case Filing	Mar. 09, 2012 Langley Gulch Power Plant Cost Recovery Fiing - Oregon	Sep. 30, 2012 Federal Open Access Transmission Tariff Rate	Jun. 30, 2012 Federal Open Access Transmission Tariff Rate
Rate Case
Increase (Decrease) in Rates			$ 34,000,000					$ 43,000,000	$ 40,400,000		$ 1,200,000			$ 58,100,000	$ 59,900,000			$ 396,600,000		$ 42,600,000		$ 42,000,000		$ 1,500,000	$ 1,600,000		$ 1,300,000	$ 10,600,000	$ 2,700,000	$ 1,800,000	$ 5,800,000	$ 3,000,000
Period of Current ADITC Stipulation				3 years
Extension period of the fixed cost adjustment pilot program										2 years
Accelerated depreciation period of metering equipment																										3 years
Authorized Rate of Return in Rate Case			7.86%																											7.757%
Total Retail Rate Base			2,360,000,000																												121,900,000
Authorized Return on Equity in Rate Case, Minimum					9.50%	9.50%																								9.90%
Authorized Return on Equity in Rate Case, Mid-point					10.00%
Authorized Return on Equity in Rate Case, Maximum					10.50%	10.50%																									10.50%
Investment Tax Credits, Maximum, in Rate Case					45,000,000
Investment Tax Credits Maximum in one Year in Rate Case					25,000,000
Automatic adjustment of authorized return on equity in rate case, minimum					95.00%
Automatic adjustment of authorized return on equity in rate case, maximum					105.00%
Percentage to be Shared with Customers					75.00%
Percentage to be Shared with Entity					25.00%
Regulatory Liabilities							27,100,000
Net PCA Rate Increase with Revenue Sharing								15,900,000
Reduction in Pension Regulatory Asset as a Result of Settlement Stipulation	13,805,000	52,068,000					20,300,000
Proposed Sharing of Costs and Benefits												50.00%
Percentage cap on the FCA adjustment												3.00%
Annual FCA Collection											10,300,000
Estimated Investment in Langley Gulch															398,000,000
Increase (Decrease) in Rate Base														335,900,000	336,700,000
Load Change Adjustment Rate Or Open Access Same Time Draft Rates													17.64			18.16	19.67																21.32	19.79
Demand-Side Management Rider Mechanism																					36,000,000
Regulatory Assets																			1,600,000		7,000,000
Jointly Owned Utility Plant, Net Ownership Amount																							22,100,000
Net Annual Transmission Revenue Requirement																																	$ 108,400,000