REVENUES: (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		$ 310,971	$ 307,779	$ 581,155	$ 643,180
Alternative revenue programs and other revenues		6,695	7,995	26,999	22,366
Derivative revenues
Disaggregation of Revenue [Line Items]
Alternative revenue programs and other revenues		2,163	413	6,274	3,132
Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		277,994	268,399	534,409	536,102
Idaho fixed cost adjustment mechanism
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	[1]	(4,532)	(7,582)	(20,725)	(19,234)
Alternative revenue programs and other revenues		4,532	7,582	20,725	19,234
Wholesale energy sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		6,866	16,158	10,775	63,373
Transmission Service Agreement
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		11,491	12,518	21,854	28,246
Energy efficiency program revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		11,953	11,458	21,428	21,570
Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		7,199	6,828	13,414	13,123
Residential Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	[1]	109,471	104,797	254,357	255,016
Residential Retail Revenue | Idaho fixed cost adjustment mechanism
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		4,135	7,233	19,844	18,543
Commercial Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	[1]	67,214	70,973	136,728	144,079
Commercial Retail Revenue | Idaho fixed cost adjustment mechanism
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		397	349	881	691
Industrial Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		43,087	45,602	85,847	91,100
Irrigation Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		60,149	48,954	61,523	49,953
Deferred revenue-AFUDC | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	[2]	(1,927)	$ (1,927)	(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] As part of its January 30, 2009, general rate case order, the IPUC is allowing 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.