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Stock Options - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands |  |  | 12 Months Ended
--- | --- | --- | ---
May 02, 2019 | May 07, 2015 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Maximum |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Option term (years) |  |  | 10 years |  |
Qualified Stock Options |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Weighted average grant date fair value of options granted (in dollars per share) |  |  | $ 38.33 | $ 39.85 | $ 38.77
Granted (in shares) |  |  | 13,950 | 12,150 | 9,500
Stock option expense |  |  | $ 500 | $ 500 | $ 500
Total unrecognized compensation cost related to non-vested share-based compensation arrangements |  |  | $ 800 |  |
Period cost is expected to be recognized (years) |  |  | 5 years |  |
Exercise of stock options (in shares) |  |  | 31,300 | 28,100 | 41,205
Non Qualified Options |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Granted (in shares) |  |  | 0 | 0 | 0
Stock option expense |  |  | $ 0 | $ 10 | $ 20
Total unrecognized compensation cost related to non-vested share-based compensation arrangements |  |  | $ 0 |  |
Exercise of stock options (in shares) |  |  | 2,300 | 34,900 | 26,800
Proceeds from stock options exercised |  |  | $ 100 | $ 1,500 | $ 1,100
Restricted Stock Units (RSUs) |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Stock option expense |  |  | 3,700 | $ 2,800 | $ 1,900
Total unrecognized compensation cost related to non-vested share-based compensation arrangements |  |  | $ 6,200 |  |
Period cost is expected to be recognized (years) |  |  | 4 years |  |
Weighted average remaining contractual life (years) |  |  | 1 year 11 months 12 days | 2 years 5 months 23 days | 2 years 6 months 10 days
Restricted Stock Units (RSUs) | Year One after Grant Date |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award |  |  |  | 25.00% | 25.00%
Award vesting period (years) |  |  | 3 years | 1 year | 1 year
Restricted Stock Units (RSUs) | Year Two after Grant Date |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award |  |  |  | 25.00% | 25.00%
Restricted Stock Units (RSUs) | Year Three after Grant Date |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award |  |  |  | 25.00% | 25.00%
Restricted Stock Units (RSUs) | Year Four after Grant Date |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award |  |  |  | 25.00% | 25.00%
Restricted Stock |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award |  |  | 50.00% |  |
Performance Shares |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award |  |  | 50.00% |  |
Option term (years) |  |  | 3 years |  |
2015 ISO Plan | Qualified Stock Options |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Shares of common stock reserved for options to be issued (in shares) |  | 400,000 |  |  |
2015 ISO Plan | Qualified Stock Options | Year One after Grant Date |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Award vesting period (years) |  | 1 year |  |  |
2015 ISO Plan | Qualified Stock Options | Year One after Grant Date | Maximum |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award |  | 20.00% |  |  |
2015 ISO Plan | Qualified Stock Options | Year Two after Grant Date |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award |  | 20.00% |  |  |
2015 ISO Plan | Qualified Stock Options | Year Three after Grant Date |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award |  | 20.00% |  |  |
2015 ISO Plan | Qualified Stock Options | Year Four after Grant Date |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award |  | 20.00% |  |  |
2015 ISO Plan | Qualified Stock Options | Year Five after Grant Date |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award |  | 20.00% |  |  |
2009 Equity Incentive Plan | Non Qualified Options |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Shares of common stock reserved for options to be issued (in shares) | 500,000 |  |  |  |
2009 Equity Incentive Plan | Non Qualified Options | Year One after Grant Date |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Award vesting period (years) | 1 year |  |  |  |
2009 Equity Incentive Plan | Non Qualified Options | Year One after Grant Date | Maximum |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award | 20.00% |  |  |  |
2009 Equity Incentive Plan | Non Qualified Options | Year Two after Grant Date |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award | 20.00% |  |  |  |
2009 Equity Incentive Plan | Non Qualified Options | Year Three after Grant Date |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award | 20.00% |  |  |  |
2009 Equity Incentive Plan | Non Qualified Options | Year Four after Grant Date |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award | 20.00% |  |  |  |
2009 Equity Incentive Plan | Non Qualified Options | Year Five after Grant Date |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Annual vesting percentage of award | 20.00% |  |  |  |

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