BENEFIT PLANS: Level 4 (Details) - USD ($)		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Plan
Defined Benefit Plan Disclosure
Service cost		$ 8,316,000	$ 9,742,000	$ 17,030,000	$ 19,485,000
Interest cost		10,560,000	9,683,000	21,156,000	19,365,000
Expected return on plan assets		(12,187,000)	(13,056,000)	(24,311,000)	(26,111,000)
Amortization of prior service cost		2,000	2,000	3,000	3,000
Amortization of net loss		3,302,000	3,394,000	6,782,000	6,788,000
Net periodic benefit cost		9,993,000	9,765,000	20,660,000	19,530,000
Regulatory deferral of net periodic benefit cost	[1]	(9,523,000)	(9,309,000)	(19,690,000)	(18,616,000)
IPUC Authorized recovered pension cost	[1]	4,289,000	4,289,000	8,577,000	8,577,000
Net periodic benefit cost recognized for financial reporting	[1],[2]	4,759,000	4,745,000	9,547,000	9,491,000
Contribution Requirement				0
Defined Benefit Plan, Contributions by Employer				10,000,000
Senior Management Security Plan
Defined Benefit Plan Disclosure
Service cost		(45,000)	(79,000)	(90,000)	(158,000)
Interest cost		1,145,000	1,061,000	2,288,000	2,124,000
Expected return on plan assets		0	0
Amortization of prior service cost		24,000	25,000	48,000	49,000
Amortization of net loss		633,000	947,000	1,266,000	1,894,000
Net periodic benefit cost		1,757,000	1,954,000	3,512,000	3,909,000
Net periodic benefit cost recognized for financial reporting	[2]	1,757,000	1,954,000	3,512,000	3,909,000
Postretirement Benefits Plan
Defined Benefit Plan Disclosure
Service cost		196,000	242,000	427,000	526,000
Interest cost		762,000	656,000	1,494,000	1,322,000
Expected return on plan assets		(557,000)	(605,000)	(1,110,000)	(1,234,000)
Amortization of prior service cost		12,000	12,000	24,000	24,000
Amortization of net loss		0	0	0	0
Net periodic benefit cost		413,000	305,000	835,000	638,000
Net periodic benefit cost recognized for financial reporting		413,000	305,000	835,000	638,000
Retirement Plan Total
Defined Benefit Plan Disclosure
Service cost		8,467,000	9,905,000	17,367,000	19,853,000
Interest cost		12,467,000	11,400,000	24,938,000	22,811,000
Expected return on plan assets		(12,744,000)	(13,661,000)	(25,421,000)	(27,345,000)
Amortization of prior service cost		38,000	39,000	75,000	76,000
Amortization of net loss		3,935,000	4,341,000	8,048,000	8,682,000
Net periodic benefit cost		12,163,000	12,024,000	25,007,000	24,077,000
Regulatory deferral of net periodic benefit cost	[1]	(9,523,000)	(9,309,000)	(19,690,000)	(18,616,000)
IPUC Authorized recovered pension cost	[1]	4,289,000	4,289,000	8,577,000	8,577,000
Net periodic benefit cost recognized for financial reporting	[1],[2]	6,929,000	7,004,000	13,894,000	14,038,000
Net Periodic Benefit cost recognize in Other operations and maintenance		4,200,000	4,100,000	8,400,000	8,200,000
Net Periodic Benefit cost recognized in other expense, net		$ 2,700,000	$ 2,900,000	$ 5,500,000	$ 5,800,000

[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 June 30, 2019 and 2018.