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REGULATORY PROCEEDINGS (Details) - USD ($)
$ in Millions
 12 Months Ended
Nov. 28, 2018
May 31, 2018
Nov. 29, 2016
May 31, 2016
Nov. 24, 2015
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Other Proceedings [Abstract]                
Cumulative DSIC Rate 5.55% 3.63% 4.71% 2.30% 1.57%      
Net Eligible Plant Improvements - Cumulative Dollars $ 30.4 $ 24.7 $ 16.6 $ 10.3 $ 7.0      
Delaware [Member]                
Water and Wastewater Rates [Abstract]                
Temporary annual rate increase subject to 15% gross water sales limitation           $ 2.5    
Percentage of gross water sales           15.00%    
Period to complete rate case by law           7 months    
Percentage of rate relief allowed should a rate case not complete           15.00%    
Refunded to customers, held in reserve           $ 3.3    
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           $ 2.8 $ 3.2 $ 1.3