BENEFIT PLANS: Level 4 (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pension Plan
Defined Benefit Plan Disclosure
Service cost		$ 8,004	$ 8,291	$ 24,014	$ 24,873
Interest cost		9,453	8,792	28,360	26,378
Expected return on plan assets		(10,519)	(10,994)	(31,560)	(31,733)
Amortization of prior service cost		15	56	44	166
Amortization of net loss		3,332	3,482	9,998	10,446
Net periodic benefit cost		10,285	9,627	30,856	30,130
Adjustments due to the effects of regulation	[1]	(5,538)	(4,902)	(16,643)	(15,873)
Net periodic benefit cost recognized for financial reporting	[1]	4,747	4,725	14,213	14,257
Contributions made to the defined benefit pension plan				40,000
Senior Management Security Plan
Defined Benefit Plan Disclosure
Service cost		307	422	921	1,267
Interest cost		1,069	967	3,206	2,901
Expected return on plan assets		0	0	0	0
Amortization of prior service cost		42	47	126	139
Amortization of net loss		883	1,048	2,649	3,146
Net periodic benefit cost		2,301	2,484	6,902	7,453
Net periodic benefit cost recognized for financial reporting		2,301	2,484	6,902	7,453
Postretirement Benefits
Defined Benefit Plan Disclosure
Service cost		279	308	837	926
Interest cost		692	670	2,075	2,009
Expected return on plan assets		(619)	(669)	(1,856)	(2,010)
Amortization of prior service cost		7	3	20	11
Amortization of net loss		0	0	0	0
Net periodic benefit cost		359	312	1,076	936
Net periodic benefit cost recognized for financial reporting		$ 359	$ 312	$ 1,076	$ 936

[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, income statement recognition of pension plan costs is deferred until costs are recovered through rates.