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Fair Value Measurements (Details) - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Interest Rate Swap [Abstract]    
Term of debt on utilities rated A- used to discount prospective cash flows 30 years  
Reduction in fair value of swap liability $ 42  
Fair Value Measurements [Abstract]    
Customers' advances for construction 6,570 $ 6,324
Note receivable 255 255
Fair Value on a Recurring Basis [Member]    
Interest Rate Swap [Abstract]    
Interest rate swap 1,720 2,196
Fair Value on a Recurring Basis [Member] | Fair Value Measurements Using Significant Other Observable Inputs (Level 2) [Member]    
Interest Rate Swap [Abstract]    
Interest rate swap 1,720 2,196
Carrying Amount [Member]    
Fair Value, Financial Liabilities [Abstract]    
Total long-term debt 94,656 92,833
Estimate of Fair Value [Member]    
Fair Value, Financial Liabilities [Abstract]    
Total long-term debt $ 103,000 $ 108,000