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REGULATORY PROCEEDINGS (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 31, 2019 | Mar. 31, 2018 | Jun. 30, 2018 | Dec. 31, 2018 | Dec. 31, 2016
Other Proceedings [Abstract] |  |  |  |  |
Cumulative DSIC Rate |  |  | 3.63% | 5.55% | 4.71%
Eligible Plant Improvements - Cumulative Dollars |  |  | $ 24.7 | $ 30.4 | $ 16.6
Delaware [Member] |  |  |  |  |
Rate Proceedings [Abstract] |  |  |  |  |
Percentage of gross water sales | 15.00% |  |  |  |
Period to complete rate case by law | 7 months |  |  |  |
Revenue held in reserve for rate relief due to TCJA impact to customers | $ 3.8 |  |  |  |
Delaware [Member] | Maximum [Member] |  |  |  |  |
Rate Proceedings [Abstract] |  |  |  |  |
Temporary annual rate increase subject to 15% gross water sales limitation | $ 2.5 |  |  |  |
Percentage of rate relief allowed should a rate case not complete | 15.00% |  |  |  |
Other Proceedings [Abstract] |  |  |  |  |
Distribution System Improvement Charge rate increase applied between base rate filings | 7.50% |  |  |  |
Distribution System Improvement Charge rate increase within a 12-month period | 5.00% |  |  |  |
Artesian Water [Member] |  |  |  |  |
Other Proceedings [Abstract] |  |  |  |  |
Revenue earned in DSIC rate increases | $ 0.9 | $ 0.7 |  |  |

X
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