REVENUES: Disaggregation of Revenue (Details) - USD ($)		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 31, 2018	Jun. 01, 2017
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		$ 1,285,286,000	$ 1,312,112,000	$ 1,320,004,000
Contract with Customer, Asset, Credit Loss Expense (Reversal)		2,600,000	3,600,000	4,700,000
Regulatory Liabilities		782,185,000	764,877,000
Regulatory Assets		1,383,059,000	1,214,174,000
Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		1,130,611,000	1,175,152,000	1,205,976,000
Idaho fixed cost adjustment mechanism
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	[1]	(36,923,000)	(35,924,000)	(18,196,000)
Wholesale energy sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		71,198,000	52,845,000	24,790,000
Transmission services (wheeling)
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		53,828,000	59,094,000	43,970,000
Energy efficiency program revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		40,128,000	35,703,000	39,241,000
Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		26,444,000	25,242,000	24,223,000
Residential Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		526,966,000	530,527,000	552,333,000
Residential Retail Revenue | Idaho fixed cost adjustment mechanism
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		35,587,000	34,624,000	17,320,000
Commercial Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		295,203,000	310,299,000	319,195,000
Commercial Retail Revenue | Idaho fixed cost adjustment mechanism
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		1,336,000	1,299,000	876,000
Industrial Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		181,372,000	190,130,000	195,124,000
Irrigation Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		135,850,000	158,001,000	150,030,000
Settlement agreement sharing mechanism | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		0	(5,025,000)	0
Deferred revenue-AFUDC | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	[2]	(8,780,000)	(8,780,000)	$ (10,706,000)
IPUC authorized AFUDC Collection HCC Relicensing - Gross | Idaho Power Company | Hells Canyon Complex
Disaggregation of Revenue [Line Items]
Regulatory Liabilities		8,800,000			$ 10,700,000	$ 10,700,000
Energy efficiency regulatory liability
Disaggregation of Revenue [Line Items]
Regulatory Liabilities	[3]	0	5,259,000
Energy efficiency regulatory asset
Disaggregation of Revenue [Line Items]
Regulatory Assets	[3]	1,465,000	$ 1,398,000
IDAHO | Energy efficiency regulatory asset
Disaggregation of Revenue [Line Items]
Regulatory Assets		300,000
OREGON | Energy efficiency regulatory asset
Disaggregation of Revenue [Line Items]
Regulatory Assets		$ 1,200,000

[1] The FCA mechanism is an alternative revenue program in the Idaho jurisdiction and does not represent revenue from contracts with customers.

[2] he IPUC allows Idaho Power to recover a portion of the AFUDC on construction work in progress related to the HCC relicensing process, even though the relicensing process is not yet complete and the costs have not been moved to electric plant in service. Idaho Power is collecting $8.8 million annually in the Idaho jurisdiction but is deferring revenue recognition of the amounts collected until the license is issued and the accumulated license costs approved for recovery are placed in service. Prior to the May 2018 Idaho Tax Reform Settlement Stipulation described in Note 3 - "Regulatory Matters," Idaho Power was collecting $10.7 million annually.

[3] The energy efficiency asset includes the Oregon jurisdiction balance at December 31, 2019 and 2018. The Idaho jurisdiction balance was an asset at December 31, 2019, and a liability at December 31, 2018.