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Commitments and Contingent Liabilities (Schedule of Purchased Water Costs) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Purchased Water |  |  |  |
Treated | $ 933 | $ 818 | $ 2,657 | $ 2,415
Untreated | 878 | 878 | 2,530 | 2,521
Total Costs | $ 1,811 | $ 1,696 | $ 5,187 | $ 4,936

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- Definition Purchased Water + References No definition available. + Details
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- Definition Refers to cost of treated water during the period. + References No definition available. + Details
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Namespace Prefix: | msex_
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Balance Type: | debit
Period Type: | duration

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- Definition Refers to cost of untreated water during the period. + References No definition available. + Details
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Namespace Prefix: | msex_
Data Type: | xbrli:monetaryItemType
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- Definition Cost of water purchased, may include any water related assessment. If water is bought on a unit volume basis, would also be considered as commodity costs. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2) -URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227 + Details
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