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