Share-Based Payment Arrangements (Narrative) (Details) $ / shares in Units, $ in Millions	3 Months Ended
Mar. 31, 2021 USD ($) entity $ / shares shares
Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, outstanding	19,510
Number of shares, exercisable	19,510
Weighted average exercise price \| $ / shares	$ 34.15
Weighted average remaining contractual term	1 year 2 months 12 days
Aggregate intrinsic value \| $	$ 0.2
Stock options exercised	3,654
Options [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of options exercised \| $	$ 0.1
Restricted and Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense \| $	$ 58.5
Weighted-average period	3 years 3 months 18 days
Total fair value of shares vested \| $	$ 0.2
Shares granted	200,335
Grant date fair value per share \| $ / shares	$ 34.31
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	60,996
Grant date fair value per share \| $ / shares	$ 38.49
Vesting performance period	3 years
Number of peer group regional banks \| entity	50
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	60,996
Grant date fair value per share \| $ / shares	$ 32.17
Vesting performance period	2 years

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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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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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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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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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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of share options (or share units) exercised during the current period.

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