Note Payable - Schedule of Notes Payable (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Debt outstanding amount	$ 33,469	$ 34,125
Term loan
Debt Instrument [Line Items]
Debt outstanding amount	33,469	34,125	$ 35,000
Less debt issuance costs	(930)	(466)	(600)
Less current portion	(875)	(875)	(875)
Note payable, net	$ 31,664	$ 32,784	$ 33,525

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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