Incentive Award Plan and Employee Benefit Plan - Summary of Restricted Share Grant Activity under Plan (Details) - Unvested shares of restricted stock, less shares assumed repurchased at market - $ / shares |
12 Months Ended | ||||
|---|---|---|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
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| Number of Target Shares | |||||
| Outstanding non-vested shares, beginning of year (in shares) | 321,627 | 346,181 | 286,917 | ||
| Shares granted (in shares) | 148,045 | 172,818 | 207,253 | ||
| Shares vested (in shares) | (182,653) | (193,373) | (137,292) | ||
| Shares forfeited (in shares) | (7,107) | (3,999) | (10,697) | ||
| Outstanding non-vested shares, end of year (in shares) | 279,912 | 321,627 | 346,181 | ||
| Weighted average price | |||||
| Outstanding non-vested shares, beginning of year (in dollars per share) | [1] | $ 40.66 | $ 45.48 | $ 53.00 | |
| Shares granted (in dollars per share) | [1] | 46.42 | 38.41 | 39.43 | |
| Shares vested (in dollars per share) | [1] | 42.04 | 47.33 | 52.11 | |
| Shares forfeited (in dollars per share) | [1] | 45.77 | 38.40 | 45.02 | |
| Outstanding non-vested shares, end of year (in dollars per share) | [1] | $ 42.67 | $ 40.66 | $ 45.48 | |
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