Capitalization (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended				12 Months Ended
	Nov. 30, 2020	Nov. 30, 2019	May 31, 2019	Feb. 28, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Aug. 31, 2019	Apr. 30, 2019	Sep. 30, 2018	Aug. 31, 2018	Mar. 31, 2018
Schedule of Capitalization [Line Items]
Issuance of Common Stock		$ 43,700
Public offering, price per share		$ 60.50
Issuance of Common Stock in a public offering, shares		800,000
Issuance of shares under the DRP					$ 1,230	$ 12,738	$ 1,150
Additional Shares Authorized By SEC To Be Issued					400,000
Preferred Stock, Shares Authorized					120,000	120,000
Preferred Stock, Shares Outstanding					20,000	20,000
Convertible preferred stock converted, value						$ 350
Amount drawn					$ 50,316	78,967	22,076
Long-term debt					277,241	234,397
Deobligated principal payments					258	130
Other long term debt					129,600	83,000
Customer advances					$ 23,404	$ 23,905
Delaware State Revolving Fund [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing amount												$ 900
All Long-term Debt [Member]
Schedule of Capitalization [Line Items]
Weighted average interest rate					3.02%	3.17%
First Mortgage Bonds - Series 2019A [Member]
Schedule of Capitalization [Line Items]
Long-term debt					$ 32,500	$ 32,500
Interest rate					4.00%
Maturity date					Aug. 01, 2059
First Mortgage Bonds - Series 2020A [Member]
Schedule of Capitalization [Line Items]
Long-term debt					$ 40,000
Interest rate					2.90%
Maturity date					Nov. 18, 2050
First Mortgage Bonds - Series 2019B [Member]
Schedule of Capitalization [Line Items]
Long-term debt					$ 21,200	$ 21,200
Interest rate					5.00%
Maturity date					Aug. 01, 2059
Convertible Preferred Stock $7.00 Series [Member]
Schedule of Capitalization [Line Items]
Percentage of stock that may be redeemed in a given calander year					10.00%
Outside Director Stock Compensation Plan [Member]
Schedule of Capitalization [Line Items]
Common stock granted and issued under plan					4,074	3,521	4,004
Maximum number of shares authorized for grant					100,000
Preferred Stock, Shares Authorized					120,000
Preferred Stock, Shares Outstanding						31,000
New Jersey Infrastructure Bank [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing capacity, construction loan										$ 8,700	$ 43,500
Percentage of principal with stated interest rate					75.00%
Percentage of principal with market interest rate					25.00%
Long-term debt					$ 89,100
Interest rate					0.00%
Construction Loan [Member]
Schedule of Capitalization [Line Items]
Interest rate					0.00%
New Jersey Board of Public Utilities (NJBPU) [Member]
Schedule of Capitalization [Line Items]
Proceeds from issuance of first mortgage bond					$ 100,000
Maturity date					Dec. 31, 2023
New Jersey Economic Development Authority [Member]
Schedule of Capitalization [Line Items]
Proceeds from issuance of first mortgage bond				$ 140,000
Maturity date				Dec. 31, 2022
New Jersey Infrastructure Bank [Member]
Schedule of Capitalization [Line Items]
Amount drawn					$ 41,900
First Mortgage Bonds [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing capacity, construction loan					60,800			$ 53,700
Amount drawn					55,100
Amount of drawn expected remaining					5,700
New Jersey Economic Development Authority [Member]
Schedule of Capitalization [Line Items]
Long-term debt					109,100
Delaware State Revolving Fund [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing amount							$ 10,000
Maximum borrowing capacity, construction loan									$ 1,700
Long-term debt					8,400
Private placement loan [Member]
Schedule of Capitalization [Line Items]
Interest rate	2.90%
Maturity date	Nov. 30, 2050
Repayment of loan	$ 40,000
Amortizing Secured Notes [Member]
Schedule of Capitalization [Line Items]
Long-term debt					30,600
Series 2018A [Member]
Schedule of Capitalization [Line Items]
Proceeds from issuance of first mortgage bond			$ 7,100
Dividend Reinvestment and Common Stock Purchase Plan [Member]
Schedule of Capitalization [Line Items]
Issuance of Common Stock					$ 1,200	$ 12,700
Dividend Reinvestment & Common Stock Purchase Plan, cumulative shares						200,000