Share-Based Payment Arrangements (Narrative) (Details) $ / shares in Units, $ in Millions	3 Months Ended
Mar. 31, 2020 USD ($) entity $ / shares shares	Mar. 31, 2019 USD ($)
Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of options exercised \| $		$ 0.5
Restricted and Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense \| $	$ 55.3
Weighted-average period	3 years 3 months 18 days
Total fair value of shares vested \| $	$ 0.2	$ 0.1
Shares granted \| shares	75,607
Grant date fair value per share \| $ / shares	$ 42.88
Performance Shares [Member] \| Executive Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	3 years
Performance Shares [Member] \| Total Shareholder Return [Member] \| Executive Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted \| shares	35,754
Grant date fair value per share \| $ / shares	$ 46.61
Vesting performance period	3 years
Number of peer group regional banks \| entity	49
Performance Shares [Member] \| Total Shareholder Return [Member] \| Executive Management [Member] \| Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of maximum number of shares vested	200.00%
Performance Shares [Member] \| Operating Earnings Per Share [Member] \| Executive Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted \| shares	35,754
Grant date fair value per share \| $ / shares	$ 39.39
Vesting performance period	2 years

Number Of Peer Group Regional Banks

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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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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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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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 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 weighted average fair value at grant date for nonvested equity-based awards issued 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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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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

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