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Fair Value of Financial Instruments (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Interest Rate Swap [Abstract]    
Term of debt on utilities rated A- used to discount prospective cash flows 30 years  
Reduction in the fair value of swap liability $ 43  
Fair Value on a Recurring Basis [Member]    
Interest Rate Swap [Abstract]    
Interest rate swap 2,196 $ 2,292
Fair Value on a Recurring Basis [Member] | Fair Value Measurements as Reporting Date Using Significant Other Observable Inputs (Level 2) [Member]    
Interest Rate Swap [Abstract]    
Interest rate swap 2,196 2,292
Carrying Amount [Member]    
Fair Value, Financial Liabilities [Abstract]    
Total long-term debt 92,833 87,488
Estimate of Fair Value [Member]    
Fair Value, Financial Liabilities [Abstract]    
Total long-term debt 108,000 99,000
Carrying Amount (Fair Value Not Accurately Estimated) [Member]    
Liabilities [Abstract]    
Customers' advances for construction 6,324 7,102
Assets [Abstract]    
Notes receivable $ 255 $ 255