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Stock-Based Compensation Plans - Stock Compensation Expense (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Stock compensation expense | $ 11,378 | $ 7,787
2007 Stock Incentive Plan |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Stock compensation expense | 3,142 | 4,584
2018 Stock Incentive Plan |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Stock compensation expense | 7,960 | 3,117
Employee Stock Purchase Plan |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Stock compensation expense | $ 276 | $ 86

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