REVENUES: (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		$ 307,779	$ 331,298	$ 643,180	$ 620,871
Alternative revenue programs and other revenues		7,995	7,401	22,366	27,289
Derivative revenues
Disaggregation of Revenue [Line Items]
Alternative revenue programs and other revenues		413	1,602	3,132	7,585
Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		268,399	298,591	536,102	563,114
Idaho fixed cost adjustment mechanism
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	[1]	(7,582)	(5,799)	(19,234)	(19,704)
Alternative revenue programs and other revenues		7,582	5,799	19,234	19,704
Wholesale energy sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		16,158	8,919	63,373	22,685
Transmission Service Agreement
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		12,518	14,500	28,246	26,198
Energy efficiency program revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		11,458	8,802	21,570	16,399
Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		6,828	6,285	13,123	12,179
Residential Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	[1]	104,797	109,155	255,016	255,838
Residential Retail Revenue | Idaho fixed cost adjustment mechanism
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		7,233	5,508	18,542	19,052
Commercial Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	[1]	70,973	76,965	144,079	151,191
Commercial Retail Revenue | Idaho fixed cost adjustment mechanism
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		349	291	692	652
Industrial Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		45,602	48,868	91,100	94,660
Irrigation Retail Revenue | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		48,954	65,065	49,953	65,471
Deferred revenue-AFUDC | Retail revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	[2]	(1,927)	$ (1,462)	(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.