Share-Based Compensation Restricted Stock Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019
Weighted Average Fair Value
Unrecognized compensation expense related to non-vested restricted stock awards	$ 8,527
Weighted average period expected for recognition of compensation expense related to non-vested restricted stock awards	1 year 8 months 12 days
Total fair value of the shares that were vested and unrestricted during the period	$ 6,493	$ 7,784
Compensation Expense, Net of Tax	3,010	2,649
Income tax benefits from compensation expense	$ 800	$ 704
Performance-based Shares Under Restriction
Share-Based Compensation
Vesting period	3 years
Shares Under Restriction
Outstanding at beginning of year (in shares)	84,105
Granted (in shares)	36,649
Vested and unrestricted (in shares)	(42,123)
Forfeited (in shares)	(6,667)
Outstanding at end of period (in shares)	71,964
Weighted Average Fair Value
Outstanding at beginning of year (in dollars per share)	$ 79.34
Granted (in dollars per share)	84.68
Vested and unrestricted (in dollars per share)	73.55
Forfeited (in dollars per share)	84.86
Outstanding at end of period (in dollars per share)	$ 84.94
Performance-based Shares Under Restriction \| Minimum
Share-Based Compensation
Actual Payouts (as a percent)	0.00%
Performance-based Shares Under Restriction \| Maximum
Share-Based Compensation
Actual Payouts (as a percent)	200.00%
Restricted Stock
Shares Under Restriction
Outstanding at beginning of year (in shares)	78,202
Granted (in shares)	34,799
Vested and unrestricted (in shares)	(43,480)
Forfeited (in shares)	(2,694)
Outstanding at end of period (in shares)	66,827
Weighted Average Fair Value
Outstanding at beginning of year (in dollars per share)	$ 79.09
Granted (in dollars per share)	90.10
Vested and unrestricted (in dollars per share)	78.07
Forfeited (in dollars per share)	87.70
Outstanding at end of period (in dollars per share)	$ 85.14
Restricted Stock \| Non-executive
Share-Based Compensation
Vesting period	5 years
Restricted Stock \| Executives and non-executives (2018 and after)
Share-Based Compensation
Vesting period	3 years
Restricted Stock \| First anniversary of grant date \| Executives and non-executives (2018 and after)
Share-Based Compensation
Actual Payouts (as a percent)	30.00%
Restricted Stock \| Second anniversary of grant date \| Executives and non-executives (2018 and after)
Share-Based Compensation
Actual Payouts (as a percent)	30.00%
Restricted Stock \| Third anniversary of grant date \| Executives and non-executives (2018 and after)
Share-Based Compensation
Actual Payouts (as a percent)	40.00%

Amount, after tax, of expense for award under share-based payment 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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Amount of tax benefit for recognition of expense of award 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 number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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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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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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

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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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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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

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