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Rate and Regulatory Matters (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended				12 Months Ended
	Oct. 31, 2017	Jun. 30, 2016	Apr. 30, 2016	Aug. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Regulatory Liabilities [Line Items]
Regulatory Liability - Cost of Utility Plant Removal					$ 43,745	$ 11,337
Acquisition premiums to be recovered					$ 500
Percentage of corporate tax regulated compaines pre-tax					92.00%
Regulatory liabilities					$ 31,600
Decrease in Regulatory assets					5,900
Middlesex [Member] | New Jersey Board Of Public Utilities [Member]
Regulatory Liabilities [Line Items]
Additional annual costs	$ 1,200
Base rate amount	$ 15,300			$ 219,000
Return on equity				9.75%
Increase in base rates revenue per year				$ 5,000
Tidewater [Member] | Delaware Public Service Commission [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues					400
Pinelands Water Company [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues			$ 200
Pinelands Wastewater [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues			$ 100
Southern Shores [Member] | Delaware Public Service Commission [Member]
Regulatory Liabilities [Line Items]
Originally filed increase in annual operating revenue					$ 100
Twin Lakes [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues		$ 100
Maximum [Member]
Regulatory Liabilities [Line Items]
Corporate tax rate					35.00%
Minimum [Member]
Regulatory Liabilities [Line Items]
Corporate tax rate					21.00%

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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