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Long-term Debt and Line of Credit - Provisions of the Term Loan (Details) - USD ($)
3 Months Ended 12 Months Ended
Dec. 31, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Aug. 05, 2015
Debt Instrument [Line Items]          
Quarterly principal payments   $ 8,200,000      
Repayments of Debt   48,111,000 $ 87,813,000 $ 63,084,000  
Current portion of debt $ 3,000,000 3,000,000      
Non-current portion of debt 55,500,000 55,500,000      
Term Loan | Line of Credit          
Debt Instrument [Line Items]          
Line of credit facility, amount outstanding 58,500,000 58,500,000      
Repayments of Debt   12,000,000      
Line of credit facility, maximum borrowing capacity 60,000,000.0 60,000,000.0      
Revolving Credit Facility          
Debt Instrument [Line Items]          
Line of credit facility, amount outstanding 22,000,000 22,000,000      
Repayments of Debt 39,900,000        
Revolving Credit Facility | Line of Credit          
Debt Instrument [Line Items]          
Line of credit facility, maximum borrowing capacity $ 65,000,000.0 $ 65,000,000.0     $ 100,000,000.0
LIBOR | Term Loan | Line of Credit          
Debt Instrument [Line Items]          
Effective interest rate 4.63% 4.63%