REVENUES: (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021		Jun. 30, 2020		Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 357,461		$ 310,971		$ 648,787	$ 581,155
Alternative revenue programs and other revenues	1,597		6,695		25,838	26,999
Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	323,161		277,994		594,612	534,409
Derivative revenues
Disaggregation of Revenue [Line Items]
Alternative revenue programs and other revenues	2,147		2,163		10,084	6,274
Idaho fixed cost adjustment mechanism
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	550	[1]	(4,532)	[1]	(15,754)	(20,725)
Alternative revenue programs and other revenues	(550)		4,532		15,754	20,725
Wholesale energy sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4,308		6,866		10,567	10,775
Transmission Service Agreement
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15,420		11,491		29,887	21,854
Energy efficiency program revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6,658		11,953		15,685	21,428
Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7,364		7,199		13,790	13,414
Residential Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	122,633	[1]	109,471	[1]	277,418	254,357
Residential Retail Revenue | Idaho fixed cost adjustment mechanism
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(715)		4,135		15,107	19,844
Commercial Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	77,609	[1]	67,214	[1]	149,878	136,728
Commercial Retail Revenue | Idaho fixed cost adjustment mechanism
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	165		397		647	881
Industrial Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	48,047		43,087		93,477	85,847
Irrigation Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	76,799		60,149		77,885	61,523
Deferred revenue-AFUDC | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(1,927)	[2]	$ (1,927)	[2]	(4,046)	$ (4,046)
IPUC authorized AFUDC Collection HCC Relicensing - Gross | Idaho Power Company | Hells Canyon Complex
Disaggregation of Revenue [Line Items]
Regulatory liabilities	$ (8,800)				$ (8,800)

[1] The FCA mechanism is an alternative revenue program in the Idaho jurisdiction and does not represent revenue from contracts with customers.

[2] The IPUC allows Idaho Power to recover a portion of the allowance for funds used during construction (AFUDC) on construction work in progress related to the Hells Canyon Complex (HCC) relicensing process, even though the relicensing process is not yet complete and the costs have not been moved to electric plant in service. Idaho Power is collecting $8.8 million annually in the Idaho jurisdiction but is deferring revenue recognition of the amounts collected until the license is issued and the accumulated license costs approved for recovery are placed in service.