REGULATORY MATTERS: Regulatory Assets and Liabilities Table (Details) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		$ 1,354,425	$ 1,242,387
Regulatory Liabilities		418,498	401,607
Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1]	170,852
Regulatory Liabilities	[1]	73,767
Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		1,183,573
Regulatory Liabilities		344,731
Income taxes [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		51,131	55,490
Income taxes [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1]	0
Income taxes [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		51,131
Removal costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[2]	183,505	180,063
Removal costs [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1],[2]	0
Removal costs [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[2]	183,505
Investment tax credits [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		79,655	79,163
Investment tax credits [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1]	0
Investment tax credits [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		79,655
Deferred revenue-AFUDC [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		87,690	72,975
Deferred revenue-AFUDC [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1]	58,835
Deferred revenue-AFUDC [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		28,855
Energy efficiency regulatory liability [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		6,554	0
Energy efficiency regulatory liability [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1]	6,554
Energy efficiency regulatory liability [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		0
Power supply costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		0	1
Power supply costs [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1]	0
Power supply costs [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		0
Settlement agreement sharing [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1]	3,159
Settlement agreement sharing [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		0
Mark-to-market liabilities / assets [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[3]	405	1,880
Mark-to-market liabilities / assets [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1],[3]	0
Mark-to-market liabilities / assets [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[3]	405
Other regulatory assets (liabilities) [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		6,399	4,036
Other regulatory assets (liabilities) [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	[1]	5,219
Other regulatory assets (liabilities) [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		1,180
Income taxes [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		875,027	802,188
Income taxes [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1]	0
Income taxes [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		875,027
Unfunded postretirement benefits [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[4]	251,762	264,548
Unfunded postretirement benefits [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1],[4]	0
Unfunded postretirement benefits [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[4]	251,762
Pension expense deferrals [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		85,790	63,644
Pension expense deferrals [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1]	62,642
Pension expense deferrals [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		23,148
Energy efficiency program costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		4,482	4,690
Energy efficiency program costs [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1]	4,482
Energy efficiency program costs [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		0
Power supply costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		47,220	59,189
Power supply costs [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1]	47,220
Power supply costs [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		0
Fixed cost adjustment
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		36,820	23,737
Fixed cost adjustment | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1]	36,820
Fixed cost adjustment | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		0
Asset retirement obligation [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[2]	14,410	17,309
Asset retirement obligation [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1],[2]	0
Asset retirement obligation [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[2]	14,410
Mark-to-market liabilities / assets [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[3]	4,973	3,961
Mark-to-market liabilities / assets [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1],[3]	0
Mark-to-market liabilities / assets [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[3]	4,973
Long-term service agreement
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		30,225	0
Long-term service agreement | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1]	18,592
Long-term service agreement | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		11,633
Other regulatory assets (liabilities) [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		3,716	3,121
Other regulatory assets (liabilities) [Member] | Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	[1]	1,096
Other regulatory assets (liabilities) [Member] | Not Earning a Return [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets		2,620
December 2011 Idaho Settlement Agreement | Settlement agreement sharing [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities		$ 3,159	$ 7,999	$ 7,600	$ 7,200

[1] Earning a return includes either interest or a return on the investment as a component of rate base at the allowed rate of return.

[2] Asset retirement obligations and removal costs are discussed in Note 13.

[3] Mark-to-market assets and liabilities are discussed in Note 16.

[4] Represents the unfunded obligation of Idaho Power’s pension and postretirement benefit plans, which are discussed in Note 11.