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Stock-Based Compensation Plans - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2020 | Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Allocated share-based compensation expense | $ 2,632 | $ 2,341
Employee Stock Purchase Plan [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Allocated share-based compensation expense | 47 | 30
Restricted Stock Awards [Member] | Non-Employee Directors [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Allocated share-based compensation expense | 160 | 170
Restricted Stock Units [Member] | Employees [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Allocated share-based compensation expense | 1,656 | 1,345
Restricted Stock Units [Member] | Independent Contractors [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Allocated share-based compensation expense | $ 769 | $ 796

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