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Long-Term Debt and Loan Agreements - Additional Information (Details) - USD ($)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
May 30, 2014
Debt Instrument [Line Items]      
Maximum borrowing capacity on line of credit $ 200,000,000    
Letters of credit $ 4,400,000    
Loan Agreement [Member]      
Debt Instrument [Line Items]      
Maximum borrowing capacity on line of credit     $ 300,000,000
Loan maturity period 2018-12    
Remaining amount available under the line of credit $ 127,700,000    
Interest rate during period 5.22% 5.20%  
Loan Agreement [Member] | Extended Maturity [Member]      
Debt Instrument [Line Items]      
Loan maturity period 2022-03