Consolidated Statement of Changes in Stockholders' Equity (Parenthetical) - $ / shares	6 Months Ended
	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