Long-Term Debt and Credit Facility (Revolving Credit Facility) (Details)	12 Months Ended
	Dec. 31, 2015 USD ($)
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 75,000,000.0
Credit facility, current borrowing capacity	62,900,000
Credit facility, remaining borrowing capacity	$ 37,800,000
Monthly facility fee	0.25%
Amount borrowed	$ 25,100,000
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 10,000,000
PNC Bank base lending rate [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Base lending rate	3.50%
Amount borrowed	$ 4,100,000
Interest rate at period end	4.00%
LIBOR [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Amount borrowed	$ 21,000,000
Interest rate at period end	1.75%
Minimum [Member] | PNC Bank base lending rate [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
Minimum [Member] | LIBOR [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.50%
Maximum [Member] | PNC Bank base lending rate [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Maximum [Member] | LIBOR [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.00%