Amount of shares earned as a % of target award.

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Share-based Compensation Arrangement by Share-based Payment Award, Award percentage attained

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Award percentage earned based on metric over the performance period.

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- Definition

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

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Number of shares issued pursuant to the terms of a deferred compensation arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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 estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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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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Equity Awards - Restricted Shares Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Unvested Restricted Shares Granted	304,138
Unrecognized Compensation Cost	$ 7.7
Period for Recognition of Share-based Compensation Cost Not yet Recognized	2 years
Restricted shares-based compensation expense	$ 5.7	$ 6.9	$ 6.2
Restricted Shares [Member] \| Non-employee independent director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares issued related to director fee deferrals	4,494	7,263	12,912
Plan 1 [Member] \| Service-based restriced shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Unvested Restricted Shares Granted	139,575	141,203	189,062
Award requisite service period	3 years
Plan 2 [Member] \| Service-based restriced shares [Member] \| Non-employee independent director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Unvested Restricted Shares Granted	25,872	25,830	30,429
Award requisite service period	1 year
Plan 3 [Member] \| Performance-based restriced shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Unvested Restricted Shares Granted	95,882
Award requisite service period	3 years
Risk-Free Interest Rate	2.29%
Expected Volatility	26.70%
Plan 5 [Member] \| Performance-based restriced shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Unvested Restricted Shares Granted		104,532
Plan 6 [Member] \| Performance-based restriced shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Unvested Restricted Shares Granted			111,761
3 year EPS CAGR metric [Member] \| Minimum [Member] \| Plan 3 [Member] \| Performance-based restriced shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount of shares earned % of target award	0.00%
3 year EPS CAGR metric [Member] \| Maximum [Member] \| Plan 3 [Member] \| Performance-based restriced shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award percentage earned based on metric over the performance period	50.00%
Amount of shares earned % of target award	200.00%
Total shareholder return metric [Member] \| Plan 4 [Member] \| Performance-based restriced shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Unvested Restricted Shares Granted	38,315
Share-based Compensation Arrangement by Share-based Payment Award, Award percentage attained		139.00%
Total shareholder return metric [Member] \| Minimum [Member] \| Plan 3 [Member] \| Performance-based restriced shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount of shares earned % of target award	0.00%
Total shareholder return metric [Member] \| Maximum [Member] \| Plan 3 [Member] \| Performance-based restriced shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award percentage earned based on metric over the performance period	50.00%
Amount of shares earned % of target award	200.00%