Share-based Compensation - Award Status (Details) - Stock option awards	6 Months Ended
Jun. 30, 2019 $ / shares shares
Shares
Outstanding at beginning of year (in shares) \| shares	87,600
Exercised (in shares) \| shares	(21,799)
Forfeited (in shares) \| shares	(2,271)
Expired (in shares) \| shares	(5,176)
Outstanding at end of year (in shares) \| shares	58,354
Exercisable at end of year (in shares) \| shares	42,472
Weighted-Average Exercise Price
Outstanding at beginning of year (in dollars per share) \| $ / shares	$ 20.58
Exercised (in dollars per share) \| $ / shares	17.71
Forfeited (in dollars per share) \| $ / shares	23.53
Expired (in dollars per share) \| $ / shares	18.13
Outstanding at end of year (in dollars per share) \| $ / shares	21.76
Exercisable at end of year (in dollars per share) \| $ / shares	$ 21.09
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	5 years 9 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	6 years 2 months 23 days

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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- Definition

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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- Definition

Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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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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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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- Definition

Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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- Definition

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

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