Purchased Receivables - Summary of Components of Net Purchased Receivables (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Jan. 01, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased receivables	$ 20,118			$ 13,995
Total	20,118			13,922
Purchased Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses - purchased receivables	$ 0	$ 0	$ 0	$ (73)	$ (87)	$ (93)	$ (94)