Long-Term Debt and Short-Term Borrowings, Debt Covenants and Restrictions (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Debt Covenants and Restrictions [Abstract]
Maximum borrowing percentage of utility plant	60.00%
Base amount added to annual net income to determine restriction on dividends and stock acquisition	$ 1,500
1.00% Pennvest Note, due 2019 [Member]
Debt Covenants and Restrictions [Abstract]
Amount of receivables pledged as collateral	$ 800