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Long-Term Debt and Loan Agreements - Additional Information (Details) - USD ($)
1 Months Ended 3 Months Ended 9 Months Ended
May 30, 2014
Mar. 31, 2017
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Dec. 31, 2019
Debt Instrument [Line Items]              
Long-term Debt     $ 78,000,000   $ 78,000,000   $ 78,000,000
Long-term Debt     $ 37,501,000   $ 37,501,000   $ 77,176,000
Weighted average interest rate during period     6.28% 6.28% 6.27% 6.26%  
Minimum [Member]              
Debt Instrument [Line Items]              
Long-term Debt     $ 11,000,000   $ 11,000,000    
Interest rate     4.67%   4.67%    
Maximum [Member]              
Debt Instrument [Line Items]              
Long-term Debt     $ 40,000,000   $ 40,000,000    
Interest rate     5.45%   5.45%    
Senior Unsecured Notes [Member]              
Debt Instrument [Line Items]              
Long-term Debt     $ 78,000,000.0   $ 78,000,000.0    
Loan Agreement [Member]              
Debt Instrument [Line Items]              
Maximum borrowing capacity on line of credit   $ 200,000,000          
Loan maturity period 2018-12 2022-03          
Remaining amount available under the line of credit     194,200,000   194,200,000    
Letters of credit     $ 5,800,000   5,800,000    
Loan Agreement [Member] | EPA [Member]              
Debt Instrument [Line Items]              
Financial assurance required to be provided         $ 2,000,000