REGULATORY MATTERS: Regulatory Requests (Details) - USD ($) $ in Thousands						12 Months Ended
		Jun. 01, 2020	Jun. 01, 2019	Jul. 01, 2017	Jun. 01, 2017	May 31, 2020	May 31, 2019	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities									$ 782,185	$ 764,877
May 2018 Tax Reform Settlement Stipulation | IDAHO
Public Utilities, General Disclosures [Line Items]
Amortization of Regulatory Asset							$ 7,400
Idaho and Oregon Rate Adjustment Request for Potential Valmy Closure | IDAHO
Public Utilities, General Disclosures [Line Items]
Approved Rate Increase (Decrease), Amount			$ 1,200		$ 13,300
Idaho and Oregon Rate Adjustment Request for Potential Valmy Closure | OREGON
Public Utilities, General Disclosures [Line Items]
Approved Rate Increase (Decrease), Amount				$ 1,100
Idaho Power Company | IDAHO
Public Utilities, General Disclosures [Line Items]
Asset Impairment Charges								$ 5,000
Energy efficiency regulatory liability
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	[1]								$ 0	$ 5,259
Post-2016 relicensing costs | Idaho Power Company | IDAHO
Public Utilities, General Disclosures [Line Items]
Asset Impairment Charges								700
Pre-2016 relicensing costs | Idaho Power Company | IDAHO
Public Utilities, General Disclosures [Line Items]
Asset Impairment Charges								4,300
Non-recurring | May 2018 Tax Reform Settlement Stipulation | IDAHO
Public Utilities, General Disclosures [Line Items]
Approved Rate Increase (Decrease), Amount							(7,800)
Non-recurring | Subsequent Event [Member] | May 2018 Tax Reform Settlement Stipulation | IDAHO
Public Utilities, General Disclosures [Line Items]
Approved Rate Increase (Decrease), Amount						$ (2,700)
Annual recurring | May 2018 Tax Reform Settlement Stipulation | IDAHO
Public Utilities, General Disclosures [Line Items]
Approved Rate Increase (Decrease), Amount							(18,700)
Annual recurring | May 2018 Tax Reform Settlement Stipulation | OREGON
Public Utilities, General Disclosures [Line Items]
Approved Rate Increase (Decrease), Amount							$ (1,500)
Annual recurring | Subsequent Event [Member] | May 2018 Tax Reform Settlement Stipulation | OREGON
Public Utilities, General Disclosures [Line Items]
Approved Rate Increase (Decrease), Amount		$ (1,500)
Maintenance and service agreements | Idaho Power Company | IDAHO
Public Utilities, General Disclosures [Line Items]
Asset Impairment Charges								2,500
Allowance for equity funds used during construction | Idaho Power Company | IDAHO
Public Utilities, General Disclosures [Line Items]
Asset Impairment Charges								$ 2,500

[1] 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.