BENEFIT PLANS: Level 4 (Details) - USD ($)		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Plan
Defined Benefit Plan Disclosure
Service cost		$ 8,516,000	$ 8,892,000	$ 25,546,000	$ 28,377,000
Interest cost		10,578,000	9,761,000	31,734,000	29,125,000
Expected return on plan assets		(12,156,000)	(13,117,000)	(36,467,000)	(39,227,000)
Amortization of prior service cost		1,000	1,000	4,000	4,000
Amortization of net loss		3,391,000	3,381,000	10,173,000	10,169,000
Net periodic benefit cost		10,330,000	8,918,000	30,990,000	28,448,000
Regulatory deferral of net periodic benefit cost	[1]	(9,845,000)	(8,498,000)	(29,534,000)	(27,114,000)
IPUC Authorized recovered pension cost	[1]	4,288,000	4,288,000	12,865,000	12,865,000
Net periodic benefit cost recognized for financial reporting	[1],[2]	4,773,000	4,708,000	14,321,000	14,199,000
Contribution Requirement				0
Defined Benefit Plan, Contributions by Employer				40,000,000
Senior Management Security Plan
Defined Benefit Plan Disclosure
Service cost		(46,000)	(79,000)	(136,000)	(237,000)
Interest cost		1,143,000	1,062,000	3,432,000	3,186,000
Expected return on plan assets		0	0	0	0
Amortization of prior service cost		24,000	24,000	72,000	73,000
Amortization of net loss		634,000	947,000	1,900,000	2,841,000
Net periodic benefit cost		1,755,000	1,954,000	5,268,000	5,863,000
Net periodic benefit cost recognized for financial reporting	[2]	1,755,000	1,954,000	5,268,000	5,863,000
Postretirement Benefits Plan
Defined Benefit Plan Disclosure
Service cost		213,000	263,000	640,000	789,000
Interest cost		748,000	660,000	2,242,000	1,982,000
Expected return on plan assets		(555,000)	(616,000)	(1,665,000)	(1,850,000)
Amortization of prior service cost		11,000	11,000	35,000	35,000
Amortization of net loss		0	0	0	0
Net periodic benefit cost		417,000	318,000	1,252,000	956,000
Net periodic benefit cost recognized for financial reporting		417,000	318,000	1,252,000	956,000
Retirement Plan Total
Defined Benefit Plan Disclosure
Service cost		8,683,000	9,076,000	26,050,000	28,929,000
Interest cost		12,469,000	11,483,000	37,408,000	34,293,000
Expected return on plan assets		(12,711,000)	(13,733,000)	(38,132,000)	(41,077,000)
Amortization of prior service cost		36,000	36,000	111,000	112,000
Amortization of net loss		4,025,000	4,328,000	12,073,000	13,010,000
Net periodic benefit cost		12,502,000	11,190,000	37,510,000	35,267,000
Regulatory deferral of net periodic benefit cost	[1]	(9,845,000)	(8,498,000)	(29,534,000)	(27,114,000)
IPUC Authorized recovered pension cost	[1]	4,288,000	4,288,000	12,865,000	12,865,000
Net periodic benefit cost recognized for financial reporting	[1],[2]	6,945,000	6,980,000	20,841,000	21,018,000
Net Periodic Benefit cost recognize in Other operations and maintenance		4,200,000	4,100,000	12,600,000	12,300,000
Net Periodic Benefit cost recognized in other expense, net		$ 2,700,000	$ 2,900,000	$ 8,200,000	$ 8,700,000

[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] Of total net periodic benefit cost recognized for financial reporting, $4.2 million and $4.1 million, respectively, were recognized in "Other operations and maintenance" and $2.7 million and $2.9 million, respectively, were recognized in "Other expense, net" on the condensed consolidated statements of income of the companies for the three months ended September 30, 2019 and 2018.