Consolidated Statements of Changes in Shareholders' Equity (Parentheticals) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee stock purchase plan (in shares)	1,351	1,362
Common Stock [Member]
Employee stock purchase plan (in shares)	1,351	1,362	2,058
Dividend reinvestment plan (in shares)	48,012	58,325	30,467
Stock option exercises (in shares)	28,082	72,711	59,117
Stock grants to directors (in shares)	11,712	13,000	20,094
Share repurchase program (in shares)		167,878	788,541
Retained Earnings [Member]
Cash dividends per common share (in dollars per share)	$ 0.74	$ 1.16	$ 0.58