BENEFIT PLANS: Schedule Defined Benefit Plans Disclosures (Details) - USD ($)		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in Fair Value of Plan Assets [Roll Forward]
Noncurrent liabilities		$ (519,570,000)	$ (431,475,000)
Less amount recorded as regulatory assets		1,383,059,000	1,214,174,000
Pension Plan
Change in Benefit Obligation [Roll Forward]
Benefit obligation at January 1		951,857,000	999,344,000
Service cost		34,061,000	37,836,000	$ 33,742,000
Interest cost		42,312,000	38,833,000	38,957,000
Actuarial (gain) loss		147,784,000	(84,758,000)
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		0	0
Benefits Paid		41,262,000	39,398,000
Projected benefit obligation at December 31		1,134,752,000	951,857,000	999,344,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value at January 1		650,604,000	697,683,000
Actual return (loss) on plan assets		113,777,000	(47,681,000)
Employer contributions		40,000,000	40,000,000
Benefits Paid		(41,262,000)	(39,398,000)
Fair value at December 31		763,119,000	650,604,000	697,683,000
Funded status at end of year		(371,633,000)	(301,253,000)
Other current liabilities		0	0
Noncurrent liabilities		(371,633,000)	(301,253,000)
Net amount recognized		(371,633,000)	(301,253,000)
Net loss		347,785,000	278,720,000
Prior service cost		56,000	62,000
Subtotal		347,841,000	278,782,000
Less amount recorded as regulatory assets	[1]	347,841,000	278,782,000
Net amount recognized in accumulated other comprehensive income		0	0
Accumulated benefit obligation		958,586,000	814,549,000
Senior Management Security Plan
Change in Benefit Obligation [Roll Forward]
Benefit obligation at January 1		102,318,000	110,303,000
Service cost		(181,000)	(316,000)	759,000
Interest cost		4,575,000	4,248,000	4,315,000
Actuarial (gain) loss		17,888,000	(7,050,000)
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		2,839,000	0
Benefits Paid		4,996,000	4,867,000
Projected benefit obligation at December 31		122,443,000	102,318,000	110,303,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value at January 1		0	0
Actual return (loss) on plan assets		0	0
Employer contributions		0	0
Benefits Paid		0	0
Fair value at December 31		0	0	$ 0
Funded status at end of year		(122,443,000)	(102,318,000)
Other current liabilities		(5,911,000)	(5,158,000)
Noncurrent liabilities		(116,532,000)	(97,160,000)
Net amount recognized		(122,443,000)	(102,318,000)
Net loss		45,851,000	30,496,000
Prior service cost		3,143,000	399,000
Subtotal		48,994,000	30,895,000
Less amount recorded as regulatory assets		0	0
Net amount recognized in accumulated other comprehensive income		48,994,000	30,895,000
Accumulated benefit obligation		$ 109,966,000	$ 94,630,000

[1] Changes in the funded status of the pension plan that would be recorded in accumulated other comprehensive income for an unregulated entity are recorded as a regulatory asset for Idaho Power as Idaho Power believes it is probable that an amount equal to the regulatory asset will be collected through the setting of future rates.