Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) (Parentheticals) - $ / shares	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Retained Earnings [Member]
Common dividends declared, per share (in dollars per share)	$ 0.36	$ 0.32
Additional Paid-in Capital [Member]
Common stock options exercised, shares (in shares)	10,350	3,566
Treasury Stock [Member]
Issuance of treasury stock to 401(k) plan, shares (in shares)	7,652	8,869
Purchase of treasury shares, shares (in shares)	474,240	10,602
Purchase of treasury shares, per share (in dollars per share)	$ 31.03	$ 24.16
Special common dividends declared, per share (in dollars per share)	0.48
Common dividends declared, per share (in dollars per share)	$ 0.84	$ 0.32

Aggregate special dividends declared during the period for each share of common stock outstanding.

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Aggregate dividends declared during the period for each share of common stock outstanding.

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Number of shares issued during the period to an employee benefit plan, such as a defined contribution or defined benefit plan.

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

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Total cost of shares repurchased divided by the total number of shares repurchased.

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Number of shares that have been repurchased during the period and are being held in treasury.

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