Consolidated Statement of Changes in Stockholders' Equity (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Common stock
Common stock transactions:
Common shares purchased and retired	21,700	20,621
Common shares issued	0	200
Non-vested common shares issued	204,991	132,531
Non-vested common shares forfeited	16,581	7,214
Stock options exercised (in shares)	67,146	112,936
Shares tendered in payment of option price and income tax withholding amounts	20,469	43,534
Retained earnings
Common stock transactions:
Common dividends (in dollars per share)	$ 0.28	$ 0.24