Interest Rate Swap Agreement (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Interest Rate Swap Agreement [Abstract]
Long-term debt	$ 84,863		$ 84,863		$ 84,885
Interest Rate Swap [Member]
Interest Rate Swap Agreement [Abstract]
Notional amount of swap	$ 12,000		$ 12,000
Fixed interest rate (in hundredths)	3.16%		3.16%
Net payment rate on swaps (in hundredths)	3.04%	3.06%	3.01%	3.03%
Interest rate swap settlements reclassified from regulatory assets to interest expense	$ 91		$ 182
Interest rate swap gain (loss) capitalized	427	$ (317)	84	$ (702)
Interest rate swap settlements to be reclassified during the next 12 months	350		350
Potential payment to counterparty	$ 2,434		$ 2,434
Maturity date of swap			Oct. 01, 2029
LIBOR [Member] | Interest Rate Swap [Member]
Interest Rate Swap Agreement [Abstract]
Percentage of variable interest rate (in hundredths)	59.00%		59.00%
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		$ 12,000