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Stock-Based Compensation Expense - Stock-Based Compensation Expense Categorized by Equity Components (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total stock-based compensation expense $ 39,135 $ 31,554 $ 31,011
Employee stock purchase plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total stock-based compensation expense 2,613 2,304 2,599
Employee stock options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total stock-based compensation expense 71 219 438
Restricted stock awards and units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total stock-based compensation expense $ 36,451 $ 29,031 $ 27,974