Share Based Compensation Plans (Changes in Stock Options Outstanding) (Details) - $ / shares	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Options
Outstanding at beginning of year (in shares)	481,381	407,832	316,423
Granted (in shares)	185,600	129,550	125,434
Exercised (in shares)	(155,769)	(43,801)	(29,975)
Lapsed or canceled (in shares)	(3,720)	(12,200)	(4,050)
Outstanding at end of year (in shares)	507,492	481,381	407,832
Options exercisable at end of year (in shares)	142,859	173,781	105,889
Weighted Average Exercise Price
Outstanding at beginning of year (in usd per share)	$ 16.52	$ 15.33	$ 14.02
Granted (in usd per share)	27.85	18.77	18.03
Exercised (in usd per share)	14.60	12.15	12.62
Lapsed or canceled (in usd per share)	15.69	16.54	16.40
Outstanding at end of year (in usd per share)	21.26	16.52	15.33
Options exercisable at end of year (in usd per share)	$ 16.65	$ 14.49	$ 12.99

Options Outstanding [Abstract]

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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.

+ References

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-Publisher FASB
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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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For presentations that combine terminations, 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 or that expired.

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Weighted average price of options that were either forfeited or expired.

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- Definition

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

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No definition available.

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

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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

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