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Debt - Additional Information (Details) - USD ($)
12 Months Ended
Feb. 12, 2019
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
May 23, 2016
Line Of Credit Facility [Line Items]          
Line of credit maximum borrowing amount   $ 300,000,000 $ 300,000,000    
Outstanding borrowings   54,600,000 99,700,000    
Debt amortization expense   168,000 163,000 $ 185,000  
Revolving Credit Facility Due 2024          
Line Of Credit Facility [Line Items]          
Line of credit maximum borrowing amount $ 300,000,000       $ 300,000,000
Line of credit facility contingent increase to maximum borrowing capacity 150,000,000        
Outstanding borrowings $ 50,000,000 $ 54,600,000 $ 99,700,000    
Commitment fee percentage per annum   0.23% 0.23%    
Revolving Credit Facility Due 2024 | Minimum          
Line Of Credit Facility [Line Items]          
Commitment fee percentage per annum 0.20%        
Revolving Credit Facility Due 2024 | Maximum          
Line Of Credit Facility [Line Items]          
Commitment fee percentage per annum 0.30%        
Revolving Credit Facility Due 2024 Swingline Sublimit          
Line Of Credit Facility [Line Items]          
Line of credit maximum borrowing amount $ 15,000,000        
Revolving Credit Facility Due 2024 Letter Of Credit Sublimit          
Line Of Credit Facility [Line Items]          
Line of credit maximum borrowing amount $ 10,000,000        
Line of Credit | Revolving Credit Facility Due 2024          
Line Of Credit Facility [Line Items]          
Debt instrument, term 5 years