Consolidated Statement of Changes in Stockholders' Equity (Parenthetical) - $ / shares	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Common stock
Common stock transactions:
Common shares purchased and retired	22,727	998,135
Common shares issued	11,267,676	16,085
Non-vested common shares issued	134,044	189,624
Non-vested common shares forfeited	30,070	25,984
Stock options exercised (in shares)	180,789	270,183
Shares tendered in payment of option price and income tax withholding amounts	56,082	94,902
Retained earnings
Cash dividends declared:
Common dividends (in dollars per share)	$ 0.72	$ 0.66