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Commitments and Contingencies - Additional Information (Details) - USD ($)
Sep. 30, 2021
Dec. 31, 2020
Sep. 30, 2020
Restricted Cash and Cash Equivalents Items [Line Items]      
Restricted funds $ 29,259,000 $ 21,644,000 $ 31,447,000
Percent of tax savings to be paid 85.00%    
Collateral with financial institutions      
Restricted Cash and Cash Equivalents Items [Line Items]      
Restricted funds $ 11,957,000 4,743,000  
Letter of Credit | Line of Credit      
Restricted Cash and Cash Equivalents Items [Line Items]      
Maximum borrowing capacity 14,900,000 7,400,000  
Letter of Credit | Line of Credit | Restricted Cash For Letters Of Credit      
Restricted Cash and Cash Equivalents Items [Line Items]      
Restricted funds 14,900,000 7,400,000  
Letter of Credit | Line of Credit | Collateral with financial institutions      
Restricted Cash and Cash Equivalents Items [Line Items]      
Restricted funds $ 14,900,000 $ 7,400,000