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Summary of Significant Accounting Policies - Contract Balances (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Accounts Receivable |  |
Accounts receivable - contracts with customers | $ 3,359 | $ 3,243
Accounts receivable - ASC 842 | 9,385 | 9,802
Total Accounts Receivable | 12,744 | 13,045
Less: Allowance for doubtful accounts | (1,150) | (1,161)
Total Accounts Receivable, net | 11,594 | 11,884
Deferred income | $ 693 | $ 1,103

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