Interest Rate Swap Agreement (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Interest Rate Swap Agreement [Abstract]
Long-term debt	$ 87,477		$ 87,488
Variable Rate Pennsylvania Economic Development Financing Authority Exempt Facilities Revenue Refunding Bonds, Series 2008A, due 2029 [Member]
Interest Rate Swap Agreement [Abstract]
Long-term debt	12,000		$ 12,000
Variable Rate Pennsylvania Economic Development Financing Authority Exempt Facilities Revenue Refunding Bonds, Series 2008A, due 2029 [Member] | Interest Rate Swap [Member]
Interest Rate Swap Agreement [Abstract]
Notional amount of swap	$ 12,000
Fixed interest rate	3.16%
Net payment rate on swap	2.64%	2.79%
Interest rate swap settlements reclassified from regulatory assets to interest expense	$ 79	$ 87
Interest rate swap loss capitalized	(9)	$ (510)
Interest rate swap settlements to be reclassified during the next 12 months	289
Potential payment to counterparty	$ 2,353
Variable Rate Pennsylvania Economic Development Financing Authority Exempt Facilities Revenue Refunding Bonds, Series 2008A, due 2029 [Member] | LIBOR [Member] | Interest Rate Swap [Member]
Interest Rate Swap Agreement [Abstract]
Percentage of variable interest rate	59.00%
Term of variable rate	1 month