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Share-Based Compensation Plan - Retainer Plan (Details) - Stock Grant Plan - Restricted stock awards - Non Employee Director - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	May 31, 2009
Share-Based Compensation
Available for future grant, at beginning	0	25,825
Retainer shares awarded	0	(13,144)
Plan Expiration		(12,681)
Available for future grant, at ending	0	0	25,825
Outstanding at beginning of period	167,319	154,175
Retainer shares awarded	0	13,144
Outstanding at end of period	167,319	167,319	154,175
Additional disclosures
Awards authorized				180,000
Compensation expense	$ 0.0	$ 0.3	$ 0.3

X

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were expired during the reporting period as a result of plan expiration.

+ References

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- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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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.

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Number of shares authorized for issuance under share-based payment arrangement.

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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