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Summary of Significant Accounting Policies - Stock-Based Compensation (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Stock-based compensation expense |  | $ 5,846 | $ 11,353 | $ 5,367
Income tax benefits |  | 1,228 | 2,384 | 1,127
Excess tax benefits (expenses) on settled share-based employee payments |  | $ (165) | $ (612) | $ 990
Restricted Stock [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Shares granted during the year |  | 45,540 | 50,061 | 40,661
Shares vested during the year |  | 56,203 | 48,228 | 53,352
Unvested shares at end of year |  | 71,706 | 93,351 | 91,998
Unrecognized compensation expense at end of year (in thousands) |  | $ 2,003 | $ 2,054 | $ 1,964
Total Shareholder Return Market-Based Awards [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Shares granted during the year |  | 47,848 | 99,214 | 80,724
Shares vested during the year | [1] | 71,299 | 106,858 | 107,342
Shares earned based on market metrics |  | 0 | 0 | 0
Unvested shares at end of year |  | 122,133 | 178,035 | 187,172
Unrecognized compensation expense at end of year (in thousands) |  | $ 2,296 | $ 3,377 | $ 3,706
Performance Shares [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Shares granted during the year |  | 47,848 | 49,609 | 40,329
Shares vested during the year |  | 35,622 | 53,454 | 53,699
Shares earned based on market metrics |  | 63,763 | 106,908 | 30,102
Unvested shares at end of year |  | 83,464 | 88,990 | 93,579
Unrecognized compensation expense at end of year (in thousands) |  | $ 1,090 | $ 2,401 | $ 1,260
[1] | The market metrics were not met during 2020, 2019 and 2018 and no TRS shares were earned during these periods.

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