Long-Term Debt and Credit Facility (Revolving Credit Facility) (Details) - Restated Revolving Credit, Term Loan and Security Agreement - USD ($)	12 Months Ended
	Dec. 31, 2017	May 10, 2013
Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 75,000,000.0
Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity		75,000,000
Credit facility, current borrowing capacity	$ 71,900,000
Credit facility, remaining borrowing capacity	$ 43,900,000
Monthly facility fee	0.25%
Amount borrowed	$ 28,000,000
Line of Credit | Revolving Credit Facility | PNC Bank base lending rate
Line of Credit Facility [Line Items]
Base lending rate	4.50%
Amount borrowed	$ 6,000,000
Interest rate at period end	6.00%
Line of Credit | Revolving Credit Facility | LIBOR
Line of Credit Facility [Line Items]
Amount borrowed	$ 22,000,000
Interest rate at period end	4.07%
Line of Credit | Revolving Credit Facility | Minimum | PNC Bank base lending rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.50%
Line of Credit | Revolving Credit Facility | Minimum | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.50%
Line of Credit | Revolving Credit Facility | Maximum | PNC Bank base lending rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.00%
Line of Credit | Revolving Credit Facility | Maximum | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate	3.00%
Letter of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 10,000,000