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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Regulatory Assets (Details) - USD ($) |  | 12 Months Ended |
--- | --- | --- | ---
Dec. 18, 2015 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 09, 2015
Regulatory Assets [Abstract] |  |  |  |  |
Amortization period of depreciation and salary study expenses |  | 5 years |  |  |
Goodwill amortization period |  | 50 years |  |  |
Amortization period of deferred acquisition costs |  | 20 years |  |  |
Amortization period of deferred franchise costs |  | 80 years |  |  |
Summary of regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |
Regulatory assets, net |  | $ 2,429,000 | $ 2,561,000 |  |
Summary of other deferred assets net of amortization [Abstract] |  |  |  |  |
Debt issuance cost |  | 1,747,000 | 1,869,000 |  |
Investment in Co Bank |  | 3,023,000 | 2,851,000 |  |
Other |  | 421,000 | 461,000 |  |
Other deferred assets |  | 5,191,000 | 5,181,000 |  |
Stock Compensation Plans [Abstract] |  |  |  |  |
Number of share authorize under equity compensation plan (in shares) |  |  |  |  | 331,500
Compensation costs | $ 137,000 | $ 183,000 | $ 135,000 | $ 123,000 |
Summary of fair value of each option grant is estimated using the Black-Scholes-Merton option pricing model [Abstract] |  |  |  |  |
Dividend Yield |  |  | 3.88% | 3.63% |
Expected Volatility |  |  | 26.50% | 26.16% |
Risk Free Interest Rate |  |  | 2.24% | 1.68% |
Expected Term |  |  | 7 years 6 months 7 days | 9 years 4 months 28 days |
Base period for calculation of expected dividend yield |  | 12 months |  |  |
Shares issued as fully vested unrestricted stock awards | 5,000 |  |  |  |
Fair market value | $ 27.38 |  |  |  |
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 |  | 6,627,000 | 5,315,000 | $ 5,336,000 |
Accounts Receivable (allowance for doubtful accounts) |  | 277,000 | 250,000 | 221,000 |
Net accounts receivable |  | 6,350,000 | 5,065,000 | 5,115,000 |
Summary of allowance for doubtful accounts [Abstract] |  |  |  |  |
Beginning balance |  | 250,000 | 221,000 | 241,000 |
Allowance adjustments |  | 205,000 | 194,000 | 180,000 |
Recoveries |  | 53,000 | 64,000 | 115,000 |
Write off of uncollectible accounts |  | (231,000) | (229,000) | (315,000) |
Ending balance |  | $ 277,000 | 250,000 | 221,000 |
Cash and Cash Equivalents [Abstract] |  |  |  |  |
Maximum maturity period of temporary cash investments considered as cash equivalents |  | 3 months |  |  |
Minimum [Member] |  |  |  |  |
Other Deferred Assets [Abstract] |  |  |  |  |
Amortization period of debt issuance costs |  | 10 years |  |  |
Maximum [Member] |  |  |  |  |
Other Deferred Assets [Abstract] |  |  |  |  |
Amortization period of debt issuance costs |  | 30 years |  |  |
Maryland [Member] |  |  |  |  |
Regulatory Assets [Abstract] |  |  |  |  |
Amortization period of regulatory rate proceedings and applications |  | five years or until the next rate increase |  |  |
Delaware [Member] | Minimum [Member] |  |  |  |  |
Regulatory Assets [Abstract] |  |  |  |  |
Amortization period of regulatory rate proceedings and applications |  | 2 years |  |  |
Delaware [Member] | Maximum [Member] |  |  |  |  |
Regulatory Assets [Abstract] |  |  |  |  |
Amortization period of regulatory rate proceedings and applications |  | 2 years 6 months |  |  |
Mountain Hill [Member] |  |  |  |  |
Summary of other deferred assets net of amortization [Abstract] |  |  |  |  |
Other |  | $ 300,000 |  |  |
Postretirement benefit obligation [Member] |  |  |  |  |
Summary of regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |
Regulatory assets, net |  | 329,000 | 384,000 |  |
Deferred income taxes [Member] |  |  |  |  |
Summary of regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |
Regulatory assets, net |  | 446,000 | 461,000 |  |
Goodwill [Member] |  |  |  |  |
Summary of regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |
Regulatory assets, net |  | 318,000 | 325,000 |  |
Deferred acquisition and franchise costs [Member] |  |  |  |  |
Summary of regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |
Regulatory assets, net |  | 720,000 | 756,000 |  |
Expense of rate and regulatory proceedings [Member] |  |  |  |  |
Summary of regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |
Regulatory assets, net |  | 616,000 | 635,000 |  |
CIAC and Other [Member] |  |  |  |  |
Summary of changes in entity's accounts receivable [Abstract] |  |  |  |  |
Contractual Amounts of Contributions In Aid of Construction Due from Developers And Other |  | 1,610,000 | 1,295,000 | 1,434,000 |
Customer accounts receivable - water [Member] |  |  |  |  |
Summary of changes in entity's accounts receivable [Abstract] |  |  |  |  |
Gross accounts receivable |  | $ 5,017,000 | $ 4,020,000 | $ 3,902,000 |
7-Year Rate [Member] |  |  |  |  |
Summary of fair value of each option grant is estimated using the Black-Scholes-Merton option pricing model [Abstract] |  |  |  |  |
Period for risk free interest rate base on treasury constant maturity rate |  |  | 7 years |  |
10-Year Rate [Member] |  |  |  |  |
Summary of fair value of each option grant is estimated using the Black-Scholes-Merton option pricing model [Abstract] |  |  |  |  |
Period for risk free interest rate base on treasury constant maturity rate |  | 10 years | 10 years | 10 years |

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- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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