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Share-Based Compensation - 2012 Equity Incentive Plan Narrative (Details) - 2012 Equity Incentive Plan | 9 Months Ended
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Sep. 30, 2020 | Sep. 30, 2019
Restricted stock units |  |
Class of Stock [Line Items] |  |
Award vesting period | 3 years |
Restricted stock units | Non-Management Trustees |  |
Class of Stock [Line Items] |  |
Award vesting period | 1 year |
Stock options and Restricted stock units |  |
Class of Stock [Line Items] |  |
Award vesting period |  | 4 years
Stock options |  |
Class of Stock [Line Items] |  |
Expiration period for stock options |  | 10 years

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- Definition Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition. + 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 (a)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (a)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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