PROPERTY, PLANT AND EQUIPMENT AND JOINTLY-OWNED PROJECTS: Property, Plant and Equipmnt Level 4 (Details)		12 Months Ended
		Dec. 31, 2015 USD ($) MWh	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Public Utility, Property, Plant and Equipment
Production		$ 2,422,175,000	$ 2,316,941,000
Transmission		1,077,065,000	1,016,207,000
Distribution		1,578,445,000	1,516,933,000
General and Other		407,779,000	398,131,000
Utility plant in service		5,485,464,000	5,248,212,000
Accumulated provision for depreciation		(1,913,927,000)	(1,841,011,000)
Utility plant in service - net		$ 3,571,537,000	$ 3,407,201,000
Average depreciation rate		2.68%	2.68%	2.69%
Fuel expense		$ 186,231,000	$ 201,241,000	$ 214,482,000
Jim Bridger Plant
Public Utility, Property, Plant and Equipment
Jointly Owned Utility Plant, Name		Jim Bridger Units 1-4
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service		$ 641,382,000
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress		46,094,000
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation		$ 296,671,000
Jointly Owned Utility Plant, Proportionate Ownership Share		33.00%
Nameplate Capacity (in MW) | MWh	[1]	771
Boardman Plant
Public Utility, Property, Plant and Equipment
Jointly Owned Utility Plant, Name		Boardman
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service		$ 81,252,000
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress		113,000
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation		$ 63,715,000
Jointly Owned Utility Plant, Proportionate Ownership Share		10.00%
Nameplate Capacity (in MW) | MWh	[1]	64
Valmy Plant
Public Utility, Property, Plant and Equipment
Jointly Owned Utility Plant, Name		Valmy Units 1 and 2
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service		$ 402,276,000
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress		1,135,000
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation		$ 184,604,000
Jointly Owned Utility Plant, Proportionate Ownership Share		50.00%
Nameplate Capacity (in MW) | MWh	[1]	284
Production
Public Utility, Property, Plant and Equipment
Average depreciation rate		2.46%	2.48%
Transmission
Public Utility, Property, Plant and Equipment
Average depreciation rate		2.01%	2.03%
Distribution
Public Utility, Property, Plant and Equipment
Average depreciation rate		2.72%	2.72%
General and Other
Public Utility, Property, Plant and Equipment
Average depreciation rate		5.62%	5.49%
Bridger Coal Company
Public Utility, Property, Plant and Equipment
Fuel expense		$ 93,000,000	$ 79,000,000	79,000,000
Idaho Power Company
Public Utility, Property, Plant and Equipment
Utility plant in service		5,485,464,000	5,248,212,000
Accumulated provision for depreciation		(1,913,927,000)	(1,841,011,000)
Utility plant in service - net		3,571,537,000	3,407,201,000
Fuel expense		$ 186,231,000	201,241,000	214,482,000
Ida-West Energy
Public Utility, Property, Plant and Equipment
Jointly Owned Utility Plant, Proportionate Ownership Share		50.00%
Marysville Hydro Partners
Public Utility, Property, Plant and Equipment
Utility plant in service - net		$ 19,000,000
Ida-West | Idaho Power Company
Public Utility, Property, Plant and Equipment
Power purchased from Ida-West		$ 8,000,000	$ 9,000,000	$ 9,000,000

[1] Idaho Power’s share of nameplate capacity.