REGULATORY MATTERS: Regulatory Assets and Liabilities Table (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		$ 1,383,059	$ 1,214,174
Regulatory Liabilities		782,185	764,877
Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1]	312,764
Regulatory Liabilities	[1]	346,460
Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		1,070,295
Regulatory Liabilities		435,725
Income taxes
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[2]	96,599	98,042
Income taxes | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1],[2]	0
Income taxes | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[2]	96,599
Depreciation-related excess deferred income taxes
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[3]	183,881	190,062
Depreciation-related excess deferred income taxes | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1],[3]	183,881
Depreciation-related excess deferred income taxes | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[3]	0
Removal costs
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[4]	185,685	183,798
Removal costs | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1],[4]	0
Removal costs | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[4]	185,685
Investment tax credits
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		94,806	92,790
Investment tax credits | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1]	0
Investment tax credits | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		94,806
Deferred revenue-AFUDC
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[5]	151,668	135,146
Deferred revenue-AFUDC | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1],[5]	109,921
Deferred revenue-AFUDC | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[5]	41,747
Energy efficiency regulatory liability
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[6]	0	5,259
Energy efficiency regulatory liability | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1],[6]	0
Energy efficiency regulatory liability | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[6]	0
Power supply costs
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[7]	48,492	42,322
Power supply costs | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1],[7]	46,022
Power supply costs | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[7]	2,470
Settlement agreement sharing mechanism
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[7]	0	5,025
Settlement agreement sharing mechanism | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1],[7]	0
Settlement agreement sharing mechanism | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[7]	0
Other regulatory assets (liabilities)
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		11,915	12,433
Other regulatory assets (liabilities) | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1]	6,636
Other regulatory assets (liabilities) | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		5,279
Tax reform accrual for future amortization [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[8]	9,139	0
Tax reform accrual for future amortization [Member] | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1],[8]	0
Tax reform accrual for future amortization [Member] | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[8]	9,139
Income taxes
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[9]	646,886	614,144
Income taxes | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1],[9]	0
Income taxes | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[9]	646,886
Unfunded postretirement benefits
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[10]	347,935	278,674
Unfunded postretirement benefits | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1],[10]	0
Unfunded postretirement benefits | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[10]	347,935
Pension expense deferrals
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[11]	172,637	147,836
Pension expense deferrals | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1],[11]	150,350
Pension expense deferrals | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[11]	22,287
Energy efficiency regulatory asset
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[6]	1,465	1,398
Energy efficiency regulatory asset | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1],[6]	1,465
Energy efficiency regulatory asset | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[6]	0
Fixed cost adjustment
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[7]	54,016	42,503
Fixed cost adjustment | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1],[7]	35,208
Fixed cost adjustment | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[7]	18,808
Valmy Plant settlements
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[7]	107,525	77,512
Valmy Plant settlements | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1],[7]	107,525
Valmy Plant settlements | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[7]	0
Asset retirement obligation
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[4]	18,835	17,655
Asset retirement obligation | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1],[4]	0
Asset retirement obligation | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[4]	18,835
Long-term service agreement
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		25,590	26,748
Long-term service agreement | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1]	15,412
Long-term service agreement | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		10,178
Other regulatory assets (liabilities)
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		8,170	$ 7,704
Other regulatory assets (liabilities) | Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1]	2,804
Other regulatory assets (liabilities) | Not Earning a Return
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		$ 5,366

[1] Earning a return includes either interest or a return on the investment as a component of rate base at the allowed rate of return.

[2] Represents the tax gross-up related to the depreciation-related excess deferred income taxes and investment tax credits included in this table and has a corresponding deferred tax asset disclosed in Note 2 - "Income Taxes."

[3] In 2017, income tax reform reduced deferred income tax assets and liabilities. For depreciation-related timing differences under the normalized tax accounting method, this reduction will flow back to customers under the statutorily prescribed average rate assumption method.

[4] Asset retirement obligations and removal costs are discussed in Note 14 - "Asset Retirement Obligations (ARO)."

[5] Idaho Power is collecting revenue in the Idaho jurisdiction for AFUDC on HCC relicensing costs but is deferring revenue recognition of the amounts collected until the license is issued and the asset is placed in service under the new license.

[6] 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.

[7] This item is discussed in more detail in this Note 3 - "Regulatory Matters."

[8] Represents amount accrued under the May 2018 Idaho Tax Reform Settlement Stipulation (described below) for the future amortization of existing or future unspecified regulatory deferrals that would otherwise be a future liability recoverable from Idaho customers.

[9] Represents flow-through income tax accounting differences which have a corresponding deferred tax liability disclosed in Note 2 - "Income Taxes."

[10] Represents the unfunded obligation of Idaho Power’s pension and postretirement benefit plans, which are discussed in Note 12 - "Benefit Plans."

[11] Idaho Power records a regulatory asset for the difference between net periodic pension cost and pension cost considered for rate-making purposes relating to Idaho Power's defined benefit pension plan. In its Idaho jurisdiction, Idaho Power’s inclusion of pension costs for the establishment of retail rates is based upon contributions made to the pension plan. This regulatory asset account represents the difference between cumulative cash contributions and amounts collected in rates. Deferred costs are amortized into expense as the amounts are provided for in Idaho retail revenues.