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Stock-Based Compensation Plans - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Allocated share-based compensation expense | $ 2,662 | $ 2,536 | $ 4,950 | $ 5,168
Employee Stock Purchase Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Allocated share-based compensation expense | 24 | 36 | 74 | 83
Restricted Stock Awards [Member] | Non-Employee Directors [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Allocated share-based compensation expense | 113 | 213 | 224 | 373
Restricted Stock Units [Member] | Employees [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Allocated share-based compensation expense | 1,747 | 1,514 | 3,201 | 3,170
Restricted Stock Units [Member] | Independent Contractors, Subsequent to Adoption of New Standard [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Allocated share-based compensation expense | $ 778 | $ 773 | $ 1,451 | $ 1,542

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