GOODWILL - Narrative (Details) - USD ($)		12 Months Ended
Oct. 01, 2020	Dec. 31, 2020
Goodwill [Line Items]
Goodwill acquired		$ 42,000,000
Goodwill disposed of		23,000,000
Impairment loss	$ 0
Natural Gas Distribution
Goodwill [Line Items]
Goodwill acquired		42,000,000
Goodwill disposed of		0
Water Distribution
Goodwill [Line Items]
Goodwill acquired		0
Goodwill disposed of		23,000,000
Water Distribution \| Hingham Water System
Goodwill [Line Items]
Goodwill disposed of		$ 23,600,000

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121556970&loc=d3e13816-109267

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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 2
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
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