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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Part 2 (Details) - USD ($) |  |  |  |  | 1 Months Ended | 12 Months Ended |
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Jun. 28, 2017 | May 03, 2017 | May 04, 2016 | Dec. 18, 2015 | Jan. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 09, 2015
Amortization period of other regulatory expense [Abstract] |  |  |  |  |  |  |  |  |  |
Depreciation and salary studies |  |  |  |  |  |  | 5 years |  |  |
Goodwill |  |  |  |  |  |  | 50 years |  |  |
Deferred acquisition costs |  |  |  |  |  |  | 20 years |  |  |
Franchise costs |  |  |  |  |  |  | 80 years |  |  |
Summary of regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |  |  |  |  |  |
Regulatory assets, net |  |  |  |  |  |  | $ 7,549,000 | $ 3,374,000 |  |
Summary of other deferred assets net of amortization [Abstract] |  |  |  |  |  |  |  |  |  |
Investment in Co Bank |  |  |  |  |  |  | 3,358,000 | 3,198,000 |  |
Other |  |  |  |  |  |  | 363,000 | 386,000 |  |
Other deferred assets |  |  |  |  |  |  | 3,721,000 | 3,584,000 |  |
Regulatory Liabilities [Abstract] |  |  |  |  |  |  |  |  |  |
Decrease in the net deferred income tax liability |  |  |  |  |  |  | 23,500,000 |  |  |
Net regulatory liability amount |  |  |  |  |  |  | 22,500,000 |  |  |
Regulatory Liabilities [Line Items] |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, net |  |  |  |  |  |  | $ 23,201,000 | $ 1,022,000 |  |
Income Tax Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Percentage of limitation on deductable interest expense |  |  |  |  |  |  | 30.00% |  |  |
Federal corporate tax rate |  |  |  |  |  |  | 34.00% | 34.00% | 34.00% |
Stock Compensation Plans [Abstract] |  |  |  |  |  |  |  |  |  |
Granted (in shares) |  |  |  |  |  |  | 0 | 0 | 0 |
Number of share authorize under equity compensation plan (in shares) |  |  |  |  |  |  |  |  |  | 331,500
Compensation costs |  |  |  |  |  |  | $ 423,000 | $ 92,000 | $ 183,000 |
Unrecognized expense related to non-vested awards of restricted shares granted |  |  |  |  |  |  | 64,000 |  |  |
Summary of fair value of each option grant is estimated using the Black-Scholes-Merton option pricing model [Abstract] |  |  |  |  |  |  |  |  |  |
Granted, restricted stock awards (in shares) |  |  | 5,000 |  |  |  |  |  |  |
Fair market value (in dollars per share) |  |  | $ 27.70 |  |  |  |  |  |  |
Award vesting period |  |  | 1 year |  |  |  |  |  |  |
Accounts Receivable [Abstract] |  |  |  |  |  |  |  |  |  |
Expense related to allowance for doubtful accounts |  |  |  |  |  |  | 200,000 | 200,000 |  |
Summary of changes in entity's accounts receivable [Abstract] |  |  |  |  |  |  |  |  |  |
Gross accounts receivable |  |  |  |  |  |  | 9,185,000 | 8,059,000 | 6,627,000 |
Less allowance for doubtful accounts |  |  |  |  |  |  | 288,000 | 263,000 | 277,000 |
Net accounts receivable |  |  |  |  |  |  | 8,897,000 | 7,796,000 | 6,350,000 |
Summary of allowance for doubtful accounts [Abstract] |  |  |  |  |  |  |  |  |  |
Beginning balance |  |  |  |  | $ 263,000 | $ 288,000 | 263,000 | 277,000 | 250,000 |
Allowance adjustments |  |  |  |  |  |  | 215,000 | 195,000 | 205,000 |
Recoveries |  |  |  |  |  |  | 41,000 | 64,000 | 53,000 |
Write off of uncollectible accounts |  |  |  |  |  |  | (231,000) | (273,000) | (231,000) |
Ending balance |  |  |  |  |  |  | $ 288,000 | 263,000 | 277,000 |
Cash and Cash Equivalents [Abstract] |  |  |  |  |  |  |  |  |  |
Maximum maturity period of temporary cash investments considered as cash equivalents |  |  |  |  |  |  | 3 months |  |  |
Minimum [Member] |  |  |  |  |  |  |  |  |  |
Amortization period of other regulatory expense [Abstract] |  |  |  |  |  |  |  |  |  |
Amortization period of debt related cost |  |  |  |  | 15 years |  |  |  |  |
Maximum [Member] |  |  |  |  |  |  |  |  |  |
Amortization period of other regulatory expense [Abstract] |  |  |  |  |  |  |  |  |  |
Amortization period of debt related cost |  |  |  |  | 25 years |  |  |  |  |
Maryland [Member] |  |  |  |  |  |  |  |  |  |
Amortization period of other regulatory expense [Abstract] |  |  |  |  |  |  |  |  |  |
Regulatory rate proceedings |  |  |  |  |  |  | 5 years |  |  |
Delaware [Member] |  |  |  |  |  |  |  |  |  |
Amortization period of other regulatory expense [Abstract] |  |  |  |  |  |  |  |  |  |
Regulatory rate proceedings |  |  |  |  |  |  | 2 years 6 months |  |  |
Unrestricted Stock [Member] | 2015 Equity Compensation Plan [Member] |  |  |  |  |  |  |  |  |  |
Summary of fair value of each option grant is estimated using the Black-Scholes-Merton option pricing model [Abstract] |  |  |  |  |  |  |  |  |  |
Shares issued as fully vested unrestricted stock awards (in shares) |  |  |  | 5,000 |  |  |  |  |  |
Fair market value (in dollars per share) |  |  |  | $ 27.38 |  |  |  |  |  |
Artesian Water [Member] |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Abstract] |  |  |  |  |  |  |  |  |  |
Contributions to postretirement benefit plan |  |  |  |  |  |  | $ 37,000 |  |  |
Class A Stock [Member] | Unrestricted Stock [Member] | 2015 Equity Compensation Plan [Member] |  |  |  |  |  |  |  |  |  |
Stock Compensation Plans [Abstract] |  |  |  |  |  |  |  |  |  |
Compensation costs | $ 250,000 |  |  |  |  |  |  |  |  |
Summary of fair value of each option grant is estimated using the Black-Scholes-Merton option pricing model [Abstract] |  |  |  |  |  |  |  |  |  |
Granted, restricted stock awards (in shares) | 6,568 |  |  |  |  |  |  |  |  |
Fair market value (in dollars per share) | $ 38.06 |  |  |  |  |  |  |  |  |
Class A Stock [Member] | Restricted Stock [Member] | 2015 Equity Compensation Plan [Member] |  |  |  |  |  |  |  |  |  |
Stock Compensation Plans [Abstract] |  |  |  |  |  |  |  |  |  |
Compensation costs |  | $ 127,000 |  |  |  |  | $ 47,000 | 92,000 |  |
Summary of fair value of each option grant is estimated using the Black-Scholes-Merton option pricing model [Abstract] |  |  |  |  |  |  |  |  |  |
Granted, restricted stock awards (in shares) |  | 5,000 |  |  |  |  |  |  |  |
Fair market value (in dollars per share) |  | $ 38.10 |  |  |  |  |  |  |  |
Award vesting period |  |  |  |  |  |  | 1 year |  |  |
Mountain Hill [Member] |  |  |  |  |  |  |  |  |  |
Summary of other deferred assets net of amortization [Abstract] |  |  |  |  |  |  |  |  |  |
Other |  |  |  |  |  |  | $ 300,000 |  |  |
Plan [Member] |  |  |  |  |  |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Federal corporate tax rate |  |  |  |  |  | 21.00% |  |  |  |
Postretirement Benefit Obligation [Member] |  |  |  |  |  |  |  |  |  |
Regulatory Liabilities [Line Items] |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, net |  |  |  |  |  |  | 112,000 | 149,000 |  |
Utility Plant Retirement Cost Obligation [Member] |  |  |  |  |  |  |  |  |  |
Regulatory Liabilities [Line Items] |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, net |  |  |  |  |  |  | 549,000 | 873,000 |  |
Deferred Income Taxes [Member] |  |  |  |  |  |  |  |  |  |
Regulatory Liabilities [Line Items] |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, net |  |  |  |  |  |  | 22,540,000 | 0 |  |
Postretirement Benefit Obligation [Member] |  |  |  |  |  |  |  |  |  |
Summary of regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |  |  |  |  |  |
Regulatory assets, net |  |  |  |  |  |  | 149,000 | 186,000 |  |
Deferred Income Taxes [Member] |  |  |  |  |  |  |  |  |  |
Summary of regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |  |  |  |  |  |
Regulatory assets, net |  |  |  |  |  |  | 416,000 | 431,000 |  |
Expense of Rate and Regulatory Proceedings [Member] |  |  |  |  |  |  |  |  |  |
Summary of regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |  |  |  |  |  |
Regulatory assets, net |  |  |  |  |  |  | 70,000 | 116,000 |  |
Debt Issuance Costs [Member] |  |  |  |  |  |  |  |  |  |
Summary of regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |  |  |  |  |  |
Regulatory assets, net |  |  |  |  |  |  | 5,965,000 | 1,648,000 |  |
Goodwill [Member] |  |  |  |  |  |  |  |  |  |
Summary of regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |  |  |  |  |  |
Regulatory assets, net |  |  |  |  |  |  | 303,000 | 310,000 |  |
Deferred Acquisition and Franchise Costs [Member] |  |  |  |  |  |  |  |  |  |
Summary of regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |  |  |  |  |  |
Regulatory assets, net |  |  |  |  |  |  | 646,000 | 683,000 |  |
Customer accounts receivable - water [Member] |  |  |  |  |  |  |  |  |  |
Summary of changes in entity's accounts receivable [Abstract] |  |  |  |  |  |  |  |  |  |
Gross accounts receivable |  |  |  |  |  |  | 5,487,000 | 5,437,000 | 5,017,000 |
Contractual amounts due from developers and other [Member] |  |  |  |  |  |  |  |  |  |
Summary of changes in entity's accounts receivable [Abstract] |  |  |  |  |  |  |  |  |  |
Gross accounts receivable |  |  |  |  |  |  | $ 3,698,000 | $ 2,622,000 | $ 1,610,000 |
Federal [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |  |  |  |
Open tax year |  |  |  |  |  |  | 2015 |  |  |
Years under federal audit |  |  |  |  |  |  |  | 2012 |  |
Federal [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |  |  |  |
Open tax year |  |  |  |  |  |  | 2017 |  |  |
Years under federal audit |  |  |  |  |  |  |  | 2014 |  |
State [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |  |  |  |
Open tax year |  |  |  |  |  |  | 2014 |  |  |
State [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |  |  |  |
Open tax year |  |  |  |  |  |  | 2017 |  |  |

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