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Amount of cash inflow from exercise of option under share-based payment arrangement.

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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.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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

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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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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Gross number of share options (or share units) granted during the period.

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Percentage of vesting of award under share-based payment arrangement.

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Expected term of 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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Number of shares issued in lieu of cash for services contributed to the entity. Number of shares includes, but is not limited to, shares issued for services contributed by vendors and founders.

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Share-Based Compensation (Narrative) (Details) $ / shares in Units, $ in Thousands			12 Months Ended
	May 22, 2019	Feb. 26, 2019	Dec. 31, 2019 USD ($) Director $ / shares shares	Dec. 31, 2018 USD ($) Director $ / shares shares	Dec. 31, 2017 USD ($) Director $ / shares shares	Dec. 31, 2016 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period			10 years
Stock options awarded			0	0	0
Unrecognized compensation expense \| $			$ 0
Aggregate intrinsic value \| $				$ 236	$ 297
Proceeds from stock options exercised \| $				$ 320	$ 413
Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value \| $ / shares			$ 29.78	$ 29.03	$ 30.88
Shares issued in lieu of cash			4,192	6,363	7,841
Number of non-employee directors \| Director			3	5	6
Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense \| $			$ 2,000
Expected recognition expense period, weighted average period in years			2 years
TSR Performance Requirement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	2 years 7 months 9 days	2 years 10 months 2 days		2 years 10 months 2 days	2 years 10 months 6 days
Risk free interest rate	2.18%	2.43%		2.39%	1.45%
Expected dividend yield	3.60%	3.20%		2.83%	2.41%
Expected stock price volatility	22.00%	21.30%		21.20%	21.90%
2015 Long-Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant			216,000
Non-employee Directors Stock Incentive Plan [Member] \| Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares of common stock awarded			8,226	7,370	8,898
Required service period			1 year	1 year	1 year
Grant date fair value \| $ / shares			$ 27.33	$ 33.90	$ 29.47
Non-employee Directors Stock Incentive Plan [Member] \| Restricted Stock Awards [Member] \| Vested Immediately [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, vesting percentage			50.00%
Restricted shares of common stock awarded			4,113	3,690	4,454
Non-employee Directors Stock Incentive Plan [Member] \| Restricted Stock Awards [Member] \| Vested After Completion of One-Year Service Requirement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, vesting percentage			50.00%
Restricted shares of common stock awarded			4,113	3,680	4,444
Management Stock Incentive Plan [Member] \| Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares of common stock awarded						12,531
Required service period			3 years	3 years	3 years
Grant date fair value \| $ / shares			$ 25.60	$ 27.76	$ 31.88
Share-based vesting date					Feb. 22, 2020
Management Stock Incentive Plan [Member] \| Restricted Stock Awards [Member] \| TSR Performance Requirement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Required service period			3 years	1 year	3 years
Management Stock Incentive Plan [Member] \| PSUs [Member] \| TSR Performance Requirement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, vesting percentage			50.00%
Management Stock Incentive Plan [Member] \| PSUs [Member] \| ROAA Performance Requirement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, vesting percentage			50.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			5 years
Maximum [Member] \| Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			3 years
Maximum [Member] \| 2015 Long-Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of grants authorized			438,076
Maximum [Member] \| Management Stock Incentive Plan [Member] \| Restricted Stock Awards [Member] \| TSR Performance Requirement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares of common stock awarded			21,970	14,877
Maximum [Member] \| Management Stock Incentive Plan [Member] \| Restricted Stock Awards [Member] \| Vested After Completion of Three-Year Service Requirement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares of common stock awarded			54,476	37,676	27,831
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			3 years
Minimum [Member] \| Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			2 years