Share-Based Compensation - 2012 Equity Incentive Plan Narrative (Details) - 2012 Equity Incentive Plan	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Stock options and Restricted stock units
Class of Stock [Line Items]
Award vesting period		4 years
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	1 year
Stock options
Class of Stock [Line Items]
Expiration period for stock options		10 years

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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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

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-Name Accounting Standards Codification
-Topic 718
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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.

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