REGULATORY MATTERS: Level 4 (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Nov. 30, 2022	May 31, 2022	May 31, 2021	Jun. 01, 2021	Jun. 01, 2020	Apr. 30, 2018	Oct. 31, 2014
Power cost adjustment mechanism | IDAHO
Regulatory Matters
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 58,700
Power cost adjustment mechanism | IDAHO | Subsequent Event
Regulatory Matters
Public Utilities, Approved Rate Increase (Decrease), Amount				$ 39,100
Idaho fixed cost adjustment mechanism
Regulatory Matters
Percentage cap on the FCA adjustment							3.00%
Idaho fixed cost adjustment mechanism | IDAHO
Regulatory Matters
Annual fixed cost adjustment mechanism deferral						$ 38,300	$ 35,500
Idaho fixed cost adjustment mechanism | IDAHO | Subsequent Event
Regulatory Matters
Public Utilities, Approved Rate Increase (Decrease), Amount				$ 2,800
October 2014 Idaho Settlement Stipulation | IDAHO
Regulatory Matters
Investment Tax Credits, Maximum, in Rate Case									$ 45,000
May 2018 Tax Reform Settlement Stipulation | IDAHO
Regulatory Matters
Minimum authorized return on equity								9.40%
Target authorized return on equity								10.00%
Settlement Stipulation - Investment Tax Credits and Idaho Sharing Mechanism [Member]
Regulatory Matters
Additional accumulated deferred investment tax credits (ADITC) amortization	$ 0	$ 0
Depreciation Rate Request | IDAHO | Subsequent Event
Regulatory Matters
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 3,900
Bridger Plant Change | IDAHO | Subsequent Event
Regulatory Matters
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 30,800
Wildfire mitigation plan costs | IDAHO | Plant in service
Regulatory Matters
Requested deferral of costs	35,000
Wildfire mitigation plan costs | IDAHO | Other Operating and Maintenance Expenses
Regulatory Matters
Requested deferral of costs	$ 47,000