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Consolidated Statement of Changes in Stockholders' Equity (Parenthetical) - $ / shares | 6 Months Ended
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Jun. 30, 2018 | Jun. 30, 2017
Common stock |  |
Common stock transactions: |  |
Common shares purchased and retired | 22,596 | 21,454
Common shares issued | 11,389 | 11,267,676
Non-vested common shares issued | 204,991 | 134,044
Non-vested common shares forfeited | 27,147 | 16,712
Stock options exercised (in shares) | 127,998 | 155,537
Shares tendered in payment of option price and income tax withholding amounts | 24,729 | 50,689
Retained earnings |  |
Common stock transactions: |  |
Common dividends (in dollars per share) | $ 0.56 | $ 0.48

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