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Share-Based Compensation - Restricted Stock Activity (Details) $ / shares in Units, $ in Millions | 9 Months Ended | 120 Months Ended
--- | --- | ---
Sep. 30, 2020 USD ($) $ / shares shares | Dec. 31, 2019 USD ($) shares
Time-Based Restricted Stock Units |  |
Number of Units |  |
Beginning balance (in shares) | 714,063 |
Granted (in shares) | 194,981 |
Vested (in shares) | (272,971) | (615,643)
Forfeited (in shares) | (11,689) |
Ending balance (in shares) | 624,384 | 714,063
Nonvested shares, aggregate intrinsic value | $ | $ 22.3 | $ 25.0
Shares vested, but not released (in shares) | 615,643 |
Shares vested, but not released, aggregate intrinsic value | $ | $ 22.0 |
Total outstanding awards (in shares) | 1,240,027 |
Total outstanding awards, aggregate intrinsic value | $ | $ 44.3 |
Performance-Based Restricted Stock Units |  |
Number of Units |  |
Beginning balance (in shares) | 57,142 |
Granted (in shares) | 0 |
Vested (in shares) | (14,286) | (14,286)
Forfeited (in shares) | 0 |
Ending balance (in shares) | 42,856 | 57,142
Nonvested shares, aggregate intrinsic value | $ | $ 1.5 | $ 2.0
Shares vested, but not released (in shares) | 28,572 |
Shares vested, but not released, aggregate intrinsic value | $ | $ 1.0 |
Total outstanding awards (in shares) | 71,428 |
Total outstanding awards, aggregate intrinsic value | $ | $ 2.5 |
Market-Based Restricted Stock Units |  |
Number of Units |  |
Beginning balance (in shares) | 779,188 |
Granted (in shares) | 108,810 |
Vested (in shares) | 0 |
Forfeited (in shares) | (14,417) |
Ending balance (in shares) | 873,581 | 779,188
Nonvested shares, aggregate intrinsic value | $ | $ 31.2 | $ 27.3
Shares vested, but not released (in shares) | 0 |
Shares vested, but not released, aggregate intrinsic value | $ | $ 0.0 |
Total outstanding awards (in shares) | 873,581 |
Total outstanding awards, aggregate intrinsic value | $ | $ 31.2 |
Resigned Trustee | Restricted Stock Units |  |
Number of Units |  |
Vested (in shares) | (14,286) |
Shares vested, but not released (in shares) | 568,753 |
Weighted average grant date fair value of vested awards (in USD per share) | $ / shares | $ 9.38 |

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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(3) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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