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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