BENEFIT PLANS: Level 4 (Details) - USD ($)	3 Months Ended				6 Months Ended
	Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017
Pension Plan
Defined Benefit Plan Disclosure
Service cost	$ 9,742,000		$ 8,245,000		$ 19,485,000		$ 16,871,000
Interest cost	9,683,000		9,716,000		19,365,000		19,479,000
Expected return on plan assets	(13,056,000)		(11,181,000)		(26,111,000)		(22,569,000)
Amortization of prior service cost	2,000		7,000		3,000		14,000
Amortization of net loss	3,394,000		3,212,000		6,788,000		6,595,000
Net periodic benefit cost	9,765,000		9,999,000		19,530,000		20,390,000
Regulatory deferral of net periodic benefit cost	(9,309,000)	[1]	(9,488,000)	[1]	(18,616,000)	[2]	(19,284,000)	[2]
IPUC Authorized recovered pension cost	4,289,000	[1]	4,289,000	[1]	8,577,000	[2]	8,577,000	[2]
Net periodic benefit cost recognized for financial reporting	4,745,000	[1],[3]	4,800,000	[1],[3]	9,491,000	[2],[4]	9,683,000	[2],[4]
Contribution Requirement					0
Defined Benefit Plan, Contributions by Employer					20,000,000
Senior Management Security Plan
Defined Benefit Plan Disclosure
Service cost	(79,000)		190,000		(158,000)		380,000
Interest cost	1,061,000		1,079,000		2,124,000		2,157,000
Expected return on plan assets	0		0		0		0
Amortization of prior service cost	25,000		32,000		49,000		64,000
Amortization of net loss	947,000		740,000		1,894,000		1,481,000
Net periodic benefit cost	1,954,000		2,041,000		3,909,000		4,082,000
Net periodic benefit cost recognized for financial reporting	1,954,000	[3]	2,041,000	[3]	3,909,000	[4]	4,082,000	[4]
Postretirement Benefits Plan
Defined Benefit Plan Disclosure
Service cost	242,000		197,000		526,000		486,000
Interest cost	656,000		702,000		1,322,000		1,392,000
Expected return on plan assets	(605,000)		(584,000)		(1,234,000)		(1,154,000)
Amortization of prior service cost	12,000		17,000		24,000		24,000
Amortization of net loss	0		0		0		0
Net periodic benefit cost	305,000		332,000		638,000		748,000
Net periodic benefit cost recognized for financial reporting	305,000		332,000		638,000		748,000
Retirement Plan Total
Defined Benefit Plan Disclosure
Service cost	9,905,000		8,632,000		19,853,000		17,737,000
Interest cost	11,400,000		11,497,000		22,811,000		23,028,000
Expected return on plan assets	(13,661,000)		(11,765,000)		(27,345,000)		(23,723,000)
Amortization of prior service cost	39,000		56,000		76,000		102,000
Amortization of net loss	4,341,000		3,952,000		8,682,000		8,076,000
Net periodic benefit cost	12,024,000		12,372,000		24,077,000		25,220,000
Regulatory deferral of net periodic benefit cost	(9,309,000)	[1]	(9,488,000)	[1]	(18,616,000)	[2]	(19,284,000)	[2]
IPUC Authorized recovered pension cost	4,289,000	[1]	4,289,000	[1]	8,577,000	[2]	8,577,000	[2]
Net periodic benefit cost recognized for financial reporting	7,004,000	[1],[3]	7,173,000	[1],[3]	14,038,000	[2],[4]	14,513,000	[2],[4]
Net Periodic Benefit cost recognize in Other operations and maintenance	4,100,000		4,400,000		8,200,000		8,900,000
Net Periodic Benefit cost recognized in other expense, net	$ 2,900,000		$ 2,800,000		$ 5,800,000		$ 5,600,000

[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] (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.

[3] (2) Of total net periodic benefit cost recognized for financial reporting, $4.1 million and $4.4 million, respectively, was recognized in "Other operations and maintenance" and $2.9 million and $2.8 million, respectively, was recognized in "Other expense, net" on the condensed consolidated statements of income of the companies for the three months ended June 30, 2018 and 2017.

[4] (2) Of total net periodic benefit cost recognized for financial reporting, $8.2 million and $8.9 million, respectively, was recognized in "Other operations and maintenance" and $5.8 million and $5.6 million, respectively, was recognized in "Other expense, net" on the condensed consolidated statements of income of the companies for the six months ended June 30, 2018 and 2017.