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Stock-Based Compensation Plans - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share-based compensation expense | $ 9,278 | $ 11,983 | $ 9,145
Employee Stock Purchase Plan [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share-based compensation expense | 139 | 109 | 128
Restricted Stock Awards [Member] | Non-Employee Directors [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share-based compensation expense | 643 | 632 | 397
Restricted Stock Units [Member] | Employees [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share-based compensation expense | 5,419 | 4,233 | 3,750
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 | $ 3,077 |  |
Restricted Stock Units [Member] | Independent Contractors, Prior to Adoption of New Standard [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Share-based compensation expense - Independent contractors |  | $ 7,009 | $ 4,870

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