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Stock-based Compensation - Expense (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019 | Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Stock-based compensation expense | $ 2.7 | $ 1.5 | $ 7.3 | $ 2.3 | $ 4.3 | $ 2.1
Other insurance expense |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Stock-based compensation expense | 0.1 | 0.2 | 0.5 | 0.4 | 0.6 | 0.2
Sales and marketing |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Stock-based compensation expense | 0.8 | 0.3 | 2.1 | 0.5 | 1.1 | 0.3
Technology development |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Stock-based compensation expense | 0.8 | 0.7 | 2.1 | 0.8 | 1.4 | 0.1
General and administrative |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Stock-based compensation expense | $ 0.9 | $ 0.3 | $ 2.4 | $ 0.6 | $ 1.2 | $ 1.5

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