BENEFIT PLANS: Level 4 (Details) - USD ($)		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2017
Pension Plan
Defined Benefit Plan Disclosure
Service cost		$ 8,245,000	$ 7,893,000	$ 16,871,000	$ 16,010,000
Interest cost		9,716,000	9,484,000	19,479,000	18,907,000
Expected return on plan assets		(11,181,000)	(10,871,000)	(22,569,000)	(21,041,000)
Amortization of prior service cost		7,000	16,000	14,000	29,000
Amortization of net loss		3,212,000	3,282,000	6,595,000	6,666,000
Net periodic benefit cost		9,999,000	9,804,000	20,390,000	20,571,000
Regulatory deferral of net periodic benefit cost	[1]	(9,488,000)	(9,375,000)	(19,284,000)	(19,682,000)
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]	4,800,000	4,718,000	9,683,000	9,466,000
Contributions made to the defined benefit pension plan				0
Pension Plan | Scenario, Forecast [Member] | Minimum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year, Description						20000000
Pension Plan | Scenario, Forecast [Member] | Maximum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year, Description						40000000
Supplemental Employee Retirement Plan
Defined Benefit Plan Disclosure
Service cost		190,000	307,000	380,000	614,000
Interest cost		1,079,000	1,068,000	2,157,000	2,137,000
Expected return on plan assets		0	0	0	0
Amortization of prior service cost		32,000	42,000	64,000	84,000
Amortization of net loss		740,000	883,000	1,481,000	1,766,000
Net periodic benefit cost		2,041,000	2,300,000	4,082,000	4,601,000
Net periodic benefit cost recognized for financial reporting		2,041,000	2,300,000	4,082,000	4,601,000
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure
Service cost		197,000	265,000	486,000	558,000
Interest cost		702,000	687,000	1,392,000	1,383,000
Expected return on plan assets		(584,000)	(617,000)	(1,154,000)	(1,237,000)
Amortization of prior service cost		17,000	6,000	24,000	13,000
Amortization of net loss		0	0	0	0
Net periodic benefit cost		332,000	341,000	748,000	717,000
Net periodic benefit cost recognized for financial reporting		$ 332,000	$ 341,000	$ 748,000	$ 717,000

[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.