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Summary of Significant Accounting Policies - Additional Information (Details) |  | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Mar. 27, 2020 | Sep. 30, 2021 USD ($) shares | Sep. 30, 2020 USD ($) shares | Jun. 30, 2020 USD ($) | Mar. 31, 2020 USD ($) | Sep. 30, 2021 USD ($) segment shares | Sep. 30, 2020 USD ($) shares | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Number of Reportable Segments | segment |  |  |  |  |  | 1 |  |  |  |
Accounts receivable |  | $ 22,131,000 |  |  |  | $ 22,131,000 |  | $ 9,806,000 |  |
Allowance for doubtful accounts |  | 1,700,000 |  |  |  | 1,700,000 |  |  |  |
Accounts Receivable, net |  | 23,800,000 |  |  |  | 23,800,000 |  |  |  |
Goodwill impairment loss |  |  |  |  |  | 0 |  | 0 |  |
Operating Loss Carryforwards |  | 29,800,000 |  |  |  | 29,800,000 |  |  |  |
Deferred Tax Assets, Valuation Allowance |  |  |  |  |  |  |  | $ 19,000,000.0 | $ 19,000,000.0 | $ 11,300,000
Gross net operating losses |  | 16,300,000 |  |  |  | 16,300,000 |  |  |  |
Reduction in valuation allowance |  | (4,900,000) |  |  |  | $ (4,900,000) |  |  |  |
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount |  | $ 14,100,000 |  |  |  |  |  |  |  |
Options and warrants excluded from the calculation of diluted shares | shares |  | 28,276 | 7,043,259 |  |  | 59,119 | 7,043,259 |  |  |
State and Local Jurisdiction [Member] |  |  |  |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Operating Loss Carryforwards |  | $ 16,500,000 |  |  |  | $ 16,500,000 |  |  |  |
Customer Concentration Risk [Member] | One Customer | Revenue from Contract with Customer [Member] |  |  |  |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Concentration Risk, Percentage |  |  |  |  |  | 10.00% | 13.00% |  |  |
Customer Concentration Risk [Member] | One Customer | Accounts Receivable |  |  |  |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Accounts Receivable, net |  | $ 3,000,000.0 | $ 2,000,000.0 |  |  | $ 3,000,000.0 | $ 2,000,000.0 |  |  |
CARES Act |  |  |  |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Percent of taxable income offset for taxable years beginning before 2021 | 100.00% |  |  |  |  | 80.00% |  |  |  |
Preliminary tax benefit related to the alternative minimum tax refund |  |  |  |  | $ 47,000 |  |  |  |  |
Additional tax benefit related to the alternative minimum tax refund |  |  |  | $ 380,000 |  |  |  |  |  |

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