Long-Term Debt and Short-Term Borrowings, Interest Rate Swap Agreement (Details) - Interest Rate Swap [Member] - Variable Rate Pennsylvania Economic Development Financing Authority Exempt Facilities Revenue Bonds Series 2008A due 2029 [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest Rate Swap Agreement [Abstract]
Notional amount of swap	$ 12,000
Potential payment to counterparty	$ 2,239
Fixed interest rate	3.16%
Net payment rate on swap	2.50%	2.86%	3.06%
Interest rate spread	0.91%	0.39%
Overall effective rate, including variable interest and swap payments	4.07%	3.55%
LIBOR [Member]
Interest Rate Swap Agreement [Abstract]
Percentage of variable interest rate	59.00%
Term of variable rate	1 month