COMMITMENTS: Commitments Level 4 (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Feb. 05, 2016 USD ($) MWh	Dec. 31, 2015 USD ($) MWh	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Long-term Purchase Commitment
Operating Leases, Rent Expense		$ 4,400	$ 5,900	$ 5,300
Bridger Coal Company
Long-term Purchase Commitment
Guarantor Obligations Total Reclamation Trust Fund		70,000
Distributions from Reclamation Trust Fund		$ 6,000
Idaho Power Company
Long-term Purchase Commitment
Range of contract length, mimimum		1 year
Range of contract length, maximum		35 years
Utilities Operating Expense, Purchased Power under Long-term Contracts		$ 131,000	$ 145,000	$ 131,000
Operating Leases, Future Minimum Payments Due, Current		233
Operating Leases, Future Minimum Payments, Due in Two Years		971
Operating Leases, Future Minimum Payments, Due in Three Years		985
Operating Leases, Future Minimum Payments, Due in Four Years		1,062
Operating Leases, Future Minimum Payments, Due in Five Years		897
Operating Leases, Future Minimum Payments, Due Thereafter		$ 12,625
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage		33.00%
IERCo guarantee of BCC reclamation obligation		$ 73,000
Idaho Power Company | Equipment, maintenance, and service agreements
Long-term Purchase Commitment
Purchase Obligation Estimated Due Current		48,707
Purchase Obligation Estimated Future Payments Due In Two Years		11,703
Purchase Obligation Estimated Future Payments Due In Three Years		14,869
Purchase Obligation Estimated Future Payments Due In Four Years		9,214
Purchase Obligation Estimated Future Payments Due In Five Years		12,095
Purchase Obligation Estimated Future Payments Due In Six Years And Thereafter		83,721
Idaho Power Company | FERC and other industry-related fees
Long-term Purchase Commitment
Purchase Obligation Estimated Due Current		12,894
Purchase Obligation Estimated Future Payments Due In Two Years		12,746
Purchase Obligation Estimated Future Payments Due In Three Years		12,746
Purchase Obligation Estimated Future Payments Due In Four Years		8,632
Purchase Obligation Estimated Future Payments Due In Five Years		5,942
Purchase Obligation Estimated Future Payments Due In Six Years And Thereafter		$ 29,708
Idaho Power Company | CSPP on-line [Member]
Long-term Purchase Commitment
Nameplate Capacity (in MW) | MWh		784
Idaho Power Company | CSPP not on-line [Member]
Long-term Purchase Commitment
Nameplate Capacity (in MW) | MWh		448
Idaho Power Company | CSPP not on-line [Member] | Subsequent Event [Member]
Long-term Purchase Commitment
Nameplate Capacity (in MW) | MWh	25
Reduction of Long-term Purchase Commitment, Amount	$ 74,000
Contract length	20 years
Idaho Power Company | Cogeneration and power production
Long-term Purchase Commitment
Purchase Obligation Estimated Due Current		$ 199,156
Purchase Obligation Estimated Future Payments Due In Two Years		233,197
Purchase Obligation Estimated Future Payments Due In Three Years		241,356
Purchase Obligation Estimated Future Payments Due In Four Years		234,772
Purchase Obligation Estimated Future Payments Due In Five Years		234,316
Purchase Obligation Estimated Future Payments Due In Six Years And Thereafter		3,592,891
Idaho Power Company | Fuel purchase commitments
Long-term Purchase Commitment
Purchase Obligation Estimated Due Current		60,122
Purchase Obligation Estimated Future Payments Due In Two Years		43,276
Purchase Obligation Estimated Future Payments Due In Three Years		16,206
Purchase Obligation Estimated Future Payments Due In Four Years		9,169
Purchase Obligation Estimated Future Payments Due In Five Years		8,833
Purchase Obligation Estimated Future Payments Due In Six Years And Thereafter		$ 114,417