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Commitments and Contingent Liabilities (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) gal	Dec. 31, 2016 USD ($)
Commitment And Contingencies [Line Items]
Period of wastewater agreement	20 years
Guarant liabilty for AWM's performance	$ 100	$ 100
Budgeted construction cost for construction program, 2018	94,000
Budgeted construction cost for construction program, 2019	94,000
Budgeted construction cost for construction program, 2010	79,000
Rental expenses under operating leases	$ 100
Rental commitment under operating lease terms	5 years
NJ Water Supply Authority [Member]
Commitment And Contingencies [Line Items]
Purchase commitment expiration date of contract	Nov. 30, 2023
Water purchase per commitment | gal	27,000
Regulated Water Authority [Member]
Commitment And Contingencies [Line Items]
Purchase commitment expiration date of contract	Feb. 27, 2021
Water purchase per commitment | gal	3,000
City of Dover [Member]
Commitment And Contingencies [Line Items]
Water purchase per commitment | gal	15,000

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- Definition

Budgeted construction cost for construction program, next year

+ References

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- Definition

Budgeted construction cost for construction program, year one.

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- Definition

Budgeted construction cost for construction program, year two

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- Definition

Commitment And Contingencies [Line Items].

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- Definition

The expiration date of a long-term purchase commitment.

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- Definition

This item represents a non-contingent liability for the fair value of an obligation to stand ready to perform over the term of a guaranty issued in the event that specified triggering events or conditions occur.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 25
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=82913062&loc=d3e11049-110243

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.15)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.15)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 25
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=82913062&loc=d3e11019-110243

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- Definition

Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

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Term of the lessor's leasing arrangement renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of units of goods that must be purchased within the specified time period of the agreement to avoid penalties or unfavorable effects on pricing, among other adverse consequences.

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- Definition

Period covered by the long-term purchase commitment, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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