Consolidated Statements of Changes in Stockholders' Equity (Unaudited) (Parentheticals) - $ / shares	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Additional Paid-in Capital [Member]
Common shares released from Employee Benefit Trust, shares (in shares)	120,684	111,470
Restricted stock unit awards vested, shares (in shares)	248,877	258,165
Exercise of stock options, shares (in shares)	600	4,400
Treasury Stock [Member] | Shares Purchased to Fund Options Exercised [Member]
Purchase of treasury shares (in shares)	445,444
Treasury Stock [Member] | Restricted Stock Awards Repurchased to Satisfy Tax Obligations [Member]
Purchase of treasury shares (in shares)	72,869	80,303
Retained Earnings [Member]
Dividends on common stock (in dollars per share)	$ 0.40	$ 0.36
Shares Purchased to Fund Options Exercised [Member]
Purchase of treasury shares (in shares)		10,000