BENEFIT PLANS: Level 4 (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended				6 Months Ended
	Jul. 31, 2020	Jun. 30, 2020		Jun. 30, 2019		Jun. 30, 2020		Jun. 30, 2019
Pension Plan
Defined Benefit Plan Disclosure
Service cost		$ 10,578		$ 8,316		$ 21,493		$ 17,030
Interest cost		9,988		10,560		20,006		21,156
Expected return on plan assets		(14,089)		(12,187)		(28,119)		(24,311)
Amortization of prior service cost		1		2		3		3
Amortization of net loss		4,296		3,302		8,663		6,782
Net periodic benefit cost		10,774		9,993		22,046		20,660
Regulatory deferral of net periodic benefit cost		(10,279)	[1]	(9,523)	[1]	(21,021)	[2]	(19,690)	[2]
IPUC Authorized recovered pension cost		4,289	[1]	4,289	[1]	8,577	[2]	8,577	[2]
Net periodic benefit cost recognized for financial reporting		4,784	[1],[3]	4,759	[1],[3]	9,602	[2],[4]	9,547	[2],[4]
Defined Benefit Plan, Contributions by Employer						10,000
Senior Management Security Plan
Defined Benefit Plan Disclosure
Service cost		53		(45)		106		(90)
Interest cost		1,087		1,145		2,175		2,288
Expected return on plan assets		0		0		0		0
Amortization of prior service cost		73		24		145		48
Amortization of net loss		933		633		1,867		1,266
Net periodic benefit cost		2,146		1,757		4,293		3,512
Net periodic benefit cost recognized for financial reporting		2,146	[3]	1,757	[3]	4,293	[4]	3,512	[4]
Postretirement Benefits Plan
Defined Benefit Plan Disclosure
Service cost		240		196		514		427
Interest cost		633		762		1,247		1,494
Expected return on plan assets		(597)		(557)		(1,202)		(1,110)
Amortization of prior service cost		12		12		24		24
Amortization of net loss		0		0		0		0
Net periodic benefit cost		288		413		583		835
Net periodic benefit cost recognized for financial reporting		288		413		583		835
Retirement Plan Total
Defined Benefit Plan Disclosure
Service cost		10,871		8,467		22,113		17,367
Interest cost		11,708		12,467		23,428		24,938
Expected return on plan assets		(14,686)		(12,744)		(29,321)		(25,421)
Amortization of prior service cost		86		38		172		75
Amortization of net loss		5,229		3,935		10,530		8,048
Net periodic benefit cost		13,208		12,163		26,922		25,007
Regulatory deferral of net periodic benefit cost		(10,279)	[1]	(9,523)	[1]	(21,021)	[2]	(19,690)	[2]
IPUC Authorized recovered pension cost		4,289	[1]	4,289	[1]	8,577	[2]	8,577	[2]
Net periodic benefit cost recognized for financial reporting		7,218	[1],[3]	6,929	[1],[3]	14,478	[2],[4]	13,894	[2],[4]
Net Periodic Benefit cost recognize in Other operations and maintenance		4,300		4,200		8,500		8,400
Net Periodic Benefit cost recognized in other expense, net		$ 3,000		$ 2,700		$ 5,900		$ 5,500
Subsequent Event | Pension Plan
Defined Benefit Plan Disclosure
Defined Benefit Plan, Contributions by Employer	$ 10,000

[1] Net periodic benefit costs for the pension plan are recognized for financial reporting based upon the authorization of each regulatory jurisdiction in which Idaho Power operates. Under IPUC order, the Idaho portion of net periodic benefit cost is recorded as a regulatory asset and is recognized in the income statement as those costs are recovered through rates.

[2] Net periodic benefit costs for the pension plan are recognized for financial reporting based upon the authorization of each regulatory jurisdiction in which Idaho Power operates. Under IPUC order, the Idaho portion of net periodic benefit cost is recorded as a regulatory asset and is recognized in the income statement as those costs are recovered through rates.

[3] Of total net periodic benefit cost recognized for financial reporting, $4.3 million and $4.2 million, respectively, were recognized in "Other operations and maintenance" and $3.0 million and $2.7 million, respectively, were recognized in "Other expense, net" on the condensed consolidated statements of income of the companies for the three months ended June 30, 2020 and 2019.

[4] Of total net periodic benefit cost recognized for financial reporting, $8.5 million and $8.4 million, respectively, were recognized in "Other operations and maintenance" and $5.9 million and $5.5 million, respectively, were recognized in "Other expense, net" on the condensed consolidated statements of income of the companies for the six months ended June 30, 2020 and 2019.