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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 |

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