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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Percentage of the value of the incentive plan in earned cash.

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Incentive Compensation Plan, Threshold Target Award for Granting Stock Award.

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Percentage of the value of the incentive plan in restriced shares.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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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 unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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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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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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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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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 Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Unvested Restricted Shares Granted	309,849
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	35,516
Unrecognized Compensation Cost	$ 7,500
Period for Recognition of Share-based Compensation Cost Not yet Recognized	2 years
Restricted shares-based compensation expense	$ 6,900	$ 6,200	$ 6,700
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	7,263	12,912	16,588
Plan 2 [Member] \| Service-based restriced shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Unvested Restricted Shares Granted			42,740
Award requisite service period		1 year
Cash value of incentive plan			80.00%
Restriced shares value of incentive plan			20.00%
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	104,532	111,761
Award requisite service period	3 years	3 years
Risk-Free Interest Rate	2.61%	1.52%
Expected Volatility	30.20%	35.60%
Plan 5 [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	25,830	30,429	41,174
Award requisite service period	1 year
Plan 9 [Member] \| Performance-based restriced shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Unvested Restricted Shares Granted			198,956
Award requisite service period			3 years
Risk-Free Interest Rate			0.96%
Expected Volatility			35.80%
Plan 7 [Member] \| Service-based restriced shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Unvested Restricted Shares Granted			2,800
Award requisite service period		1 year
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	141,203	189,062	235,251
Award requisite service period	3 years
Minimum [Member] \| Plan 2 [Member] \| Service-based restriced shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
ICP, Threshold target for granting stock awards			$ 20
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%	40.00%
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%	50.00%
Amount of shares earned % of target award	200.00%	200.00%
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%	0.00%
Total shareholder return metric [Member] \| Minimum [Member] \| Plan 4 [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				0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award percentage attained		126.90%
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	31,021
Total shareholder return metric [Member] \| Minimum [Member] \| Plan 9 [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			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%	50.00%
Amount of shares earned % of target award	200.00%	200.00%
Total shareholder return metric [Member] \| Maximum [Member] \| Plan 4 [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				200.00%
Total shareholder return metric [Member] \| Maximum [Member] \| Plan 9 [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			200.00%