Long-Term Debt and Credit Facility (Revolving Credit Facility) (Details) - Restated Revolving Credit, Term Loan and Security Agreement - USD ($)	12 Months Ended
	Dec. 31, 2018	Jun. 13, 2018	May 10, 2013
Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 75,000,000	$ 75,000,000
Credit facility, remaining borrowing capacity	$ 25,100,000
Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity			75,000,000
Credit facility, current borrowing capacity	66,600,000
Credit facility, remaining borrowing capacity	$ 16,800,000
Monthly facility fee	0.25%
Amount borrowed	$ 49,700,000
Line of Credit | Revolving Credit Facility | PNC Bank base lending rate
Line of Credit Facility [Line Items]
Base lending rate	5.50%
Amount borrowed	$ (300,000)
Interest rate at period end	7.50%
Line of Credit | Revolving Credit Facility | LIBOR
Line of Credit Facility [Line Items]
Amount borrowed	$ 50,000,000.0
Interest rate at period end	5.51%
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