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Regulatory Matters - Additional Information (Details) - FERC - USD ($)
$ in Millions
 1 Months Ended 12 Months Ended
Jan. 31, 2017
Dec. 31, 2016
Public Utilities, General Disclosures [Line Items]    
Requested return on equity (percent) 10.70%  
Requested equity capital structure (percent) 48.00%  
RECO    
Public Utilities, General Disclosures [Line Items]    
Requested rate increase, amount $ 19.7 $ 11.8