Summary of Significant Accounting Policies - Schedule of Settlement and Merchant Reserve Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Settlement And Merchant Reserve Assets And Liabilities [Abstract]
Settlement assets	$ 141,957	$ 149,785
Merchant reserve assets	16,968	16,246
Total	158,925	166,031	$ 133,961
Settlement liabilities	140,340	148,818
Merchant reserve liabilities	16,968	16,246
Total	$ 157,308	$ 165,064