Consolidated Statements of Changes in Stockholders' Equity (Parentheticals) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retained Earnings [Member]
Common dividends declared, per share (in dollars per share)	$ 0.78	$ 0.68	$ 0.60
Special common dividends declared, per share (in dollars per share)	$ 0.48
Treasury Stock [Member]
Common stock options exercised, shares (in shares)	24,186	16,185	43,463
Issuance of treasury stock to 401(k) plan, shares (in shares)	11,331	15,254	18,218
Purchase of treasury shares, shares (in shares)	1,060,312	50,118	1,182,294
Purchase of treasury shares, per share (in dollars per share)	$ 32.45	$ 25.16	$ 20.06
Common dividends declared, per share (in dollars per share)	$ 1.26	$ 0.68	$ 0.60
Common stock options exercised, shares (in shares)	24,186