Note 3 - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Outstanding-Number of options (in shares)	82,875	88,375
Outstanding-Weighted average exercise price (in dollars per share)	$ 24.33	$ 23.27
Granted-Number of options (in shares)	23,500	21,000
Granted-Weighted average exercise price (in dollars per share)	$ 30.40	$ 29.25
Exercised-Number of options (in shares)	(17,980)	(11,650)
Exercised-Weighted average exercise price (in dollars per share)	$ 20.66	$ 17.73
Forfeited-Number of options (in shares)	(9,725)	(12,650)
Forfeited-Weighted average exercise price (in dollars per share)	$ 25.61	$ 31.87
Outstanding ending-Number of options (in shares)	78,670	85,075
Outstanding ending-Weighted average exercise price (in dollars per share)	$ 26.82	$ 24.22
Outstanding ending-Weighted average remaining contractual term	2 years 361 days	2 years 270 days
Outstanding ending-Aggregate intrinsic value	$ 407	$ 440
Exercisable-Number of options (in shares)	23,545	30,875
Exercisable-Weighted average exercise price (in dollars per share)	$ 22.38	$ 20.85
Exercisable-Weighted average remaining contractual term	1 year 43 days	1 year 43 days
Exercisable-Aggregate intrinsic value	$ 226	$ 264