REGULATORY MATTERS: Idaho Base Rate Changes (Details) - USD ($) $ in Thousands	Jun. 01, 2019	Jun. 01, 2017	Jul. 01, 2012	Jan. 01, 2012	Dec. 31, 2019	Dec. 31, 2018
Idaho Base Rate Changes [Line Items]
Regulatory Liabilities					$ 782,185	$ 764,877
2011 Idaho General Rate Case Settlement
Idaho Base Rate Changes [Line Items]
Authorized Rate of Return in Rate Case				7.86%
Total Retail Rate Base				$ 2,360,000
Approved Rate Increase (Decrease), Percentage				4.07%
Approved Rate Increase (Decrease), Amount				$ 34,000
IDAHO | Base rate adjustment request for potential Valmy closure [Member] [Member]
Idaho Base Rate Changes [Line Items]
Approved Rate Increase (Decrease), Amount	$ 1,200	$ 13,300
IDAHO | 2011 Idaho General Rate Case Settlement
Idaho Base Rate Changes [Line Items]
Approved Rate Increase (Decrease), Amount			$ 58,100
Increase (Decrease) In Rate Base			$ 335,900