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REGULATORY MATTERS (Details)
$ in Millions
1 Months Ended 12 Months Ended
Oct. 31, 2016
USD ($)
Dec. 31, 2016
USD ($)
regulatory_commission
Nov. 30, 2014
USD ($)
Public Utilities, General Disclosures [Line Items]      
Number of regulatory commissions | regulatory_commission   2  
Public Service Commission of Utah and Wyoming Public Service Commission | Filing for Gas Cost Increase, Effective November 1, 2016      
Public Utilities, General Disclosures [Line Items]      
Amount spent under program $ 8.7    
Utah Commission | Infrastructure Cost Tracking Mechanism      
Public Utilities, General Disclosures [Line Items]      
Allowed recovery amount per year   $ 70.0  
Utah Commission | Infrastructure Cost Tracking Mechanism | Minimum      
Public Utilities, General Disclosures [Line Items]      
Amount invested in new pipelines     $ 84.0