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Capitalization (Narrative) (Details) - USD ($) $ in Thousands | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Aug. 31, 2019 | Jan. 31, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019 | Apr. 30, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Aug. 31, 2018 | May 31, 2018 | Mar. 31, 2018
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of shares under the DRP, shares |  |  |  |  | 14,223 | 221,558 |  |  |  |  |  |  |
Issuance of shares under the DRP |  |  | $ 313 | $ 5,368 | $ 921 | $ 12,449 |  |  |  |  |  |  |
Common stock granted and issued under plan |  | 200,000 |  |  |  |  |  |  |  |  |  |  |
Percentage of offering shares on discount to participants |  | 5.00% |  |  |  |  |  |  |  |  |  |  |
Other long term debt |  |  | 90,900 |  | 90,900 |  | $ 83,000 |  |  |  |  |  |
Customer advances |  |  | 25,100 |  | 25,100 |  | $ 23,905 |  |  |  |  |  |
Amount drawn |  |  |  |  | 10,319 | $ 82,446 |  |  |  |  |  |  |
Middlesex [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity, construction loan |  |  | 41,900 |  | 41,900 |  |  |  |  |  |  |  |
Proceeds from private placement |  |  |  |  | 40,000 |  |  |  |  |  |  |  |
Middlesex [Member] | New Jersey Board Of Public Utilities [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing amount |  |  | $ 100,000 |  | $ 100,000 |  |  |  |  |  |  |  |
FMB [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of principal with stated interest rate |  |  |  |  | 2.90% |  |  |  |  |  |  |  |
Debt Instrument Maturity Date |  |  |  |  | Nov. 30, 2050 |  |  |  |  |  |  |  |
New Jersey Infrastructure Bank [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity, construction loan |  |  |  |  |  |  |  |  |  |  | $ 43,500 |  |
Interest rate |  |  | 0.00% |  | 0.00% |  |  |  |  |  |  |  |
Percentage of principal with stated interest rate |  |  |  |  | 75.00% |  |  |  |  |  |  |  |
Percentage of principal with market interest rate |  |  |  |  | 25.00% |  |  |  |  |  |  |  |
First Mortgage Bonds [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance premium | $ 7,100 |  |  |  |  |  |  |  |  |  |  |  |
New Jersey NJIB Program [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity, construction loan |  |  |  |  |  |  |  |  |  | $ 8,700 |  |  |
Delaware State Revolving Fund [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing amount |  |  |  |  |  |  |  |  | $ 10,000 |  |  |  | $ 900
Maximum borrowing capacity, construction loan |  |  |  |  |  |  |  | $ 1,700 |  |  |  |  |
Series 2018A [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  |  |  |  |  |  |  |  | 0.00% |
Series 2019A [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity, construction loan | $ 32,500 |  |  |  |  |  |  |  |  |  |  |  |
Interest rate | 4.00% |  |  |  |  |  |  |  |  |  |  |  |
Series 2019B [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity, construction loan | $ 21,200 |  |  |  |  |  |  |  |  |  |  |  |
Interest rate | 5.00% |  |  |  |  |  |  |  |  |  |  |  |
First Mortgage Bonds [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity, construction loan | $ 53,700 |  | $ 60,800 |  | $ 60,800 |  |  |  |  |  |  |  |
Amount drawn |  |  |  |  | 38,100 |  |  |  |  |  |  |  |
Amount of drawn expected remaining |  |  |  |  | $ 22,700 |  |  |  |  |  |  |  |

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