XML 53 R38.htm IDEA: XBRL DOCUMENT v3.3.1.900
Commitments and Contingent Liabilities (Narrative) (Details)
gal in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2015
USD ($)
gal
Dec. 31, 2014
USD ($)
Commitment And Contingencies [Line Items]    
Period of wastewater agreement 20 years  
Term of water and wastewater system agreement USA-PA operates the City of Perth Amboy, NJ's water and wastewater systems under a 20-year agreement, which expires in 2018. In connection with the agreement with Perth Amboy, USA-PA entered into a 20-year subcontract with a wastewater operating company  
Guarant liabilty for AWM's performance $ 0.2 $ 0.3
Budgeted construction cost for construction program, 2016 47.3  
Budgeted construction cost for construction program, 2017 45.4  
Budgeted construction cost for construction program, 2018 $ 67.0  
NJ Water Supply Authority [Member]    
Commitment And Contingencies [Line Items]    
Commitment of purchase of untreated water Middlesex has an agreement with the NJWSA for the purchase of untreated water through November 30, 2023, which provides for an average purchase of 27 million gallons a day (mgd). Pricing is set annually by the NJWSA through a public rate making process.  
Purchase commitment expiration date of contract Nov. 30, 2023  
Water purchase per commitment | gal 27.0  
Regulated Water Authority [Member]    
Commitment And Contingencies [Line Items]    
Minimum treated water purchase commitment Middlesex also has an agreement with a non-affiliated regulated water utility for the purchase of treated water. This agreement, which expires February 27, 2016, provides for the minimum purchase of 3 mgd of treated water with provisions for additional purchases.  
Purchase commitment expiration date of contract Feb. 27, 2021  
Water purchase per commitment | gal 3.0  
City of Dover [Member]    
Commitment And Contingencies [Line Items]    
Water purchase per commitment | gal 15.0