Note 12 - Non-vested Restricted Stock Options (Details) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Restricted Stock [Member]
Restricted stock at January 1, 2014 (in shares)	76,574	0
Restricted stock at January 1, 2014 (in dollars per share)	$ 69.27	$ 0
Granted (in shares)		77,647
Granted, weighted-average grant date fair value (in dollars per share)		$ 69.18
Restrictions lapsed (in shares)		(798)
Restrictions lapsed (in dollars per share)		$ 62.68
Forfeited (in shares)		(275)
Forfeited, weighted-average grant date fair value (in dollars per share)		$ 62.68
Restricted stock at December 31, 2014 (in shares)		76,574
Restricted stock at December 31, 2014 (in dollars per share)		$ 69.27
Granted (in shares)	68,580
Granted, weighted-average grant date fair value (in dollars per share)	$ 68.89
Restrictions lapsed (in shares)	(16,863)
Restrictions lapsed (in dollars per share)	$ 69.25
Forfeited (in shares)	(3,898)
Forfeited, weighted-average grant date fair value (in dollars per share)	$ 72.14
Restricted stock at December 31, 2014 (in shares)	124,393
Restricted stock at December 31, 2014 (in dollars per share)	$ 68.97