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Environmental Matters - Additional Information (Detail) - Environmental Restoration Costs $ in Millions | 9 Months Ended
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Sep. 30, 2020 USD ($)
Maine |
Site Contingency [Line Items] |
Amortization period for environmental costs | 5 years
New Hampshire |
Site Contingency [Line Items] |
Amortization period for environmental costs | 7 years
Northern Utilities Manufactured Gas Plant Sites |
Site Contingency [Line Items] |
Estimated Costs Accrued For Remediation | $ 0.8

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- Definition The charge against earnings in the period for known or estimated future costs arising from requirements to perform environmental remediation activities. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=109237650&loc=d3e13064-110858 Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 12 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13296-110859 + Details
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