Note 3 - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Outstanding-Number of options (in shares)	82,875	88,375
Granted-Number of options (in shares)	23,500	21,000
Exercised-Number of options (in shares)	(18,425)	(12,150)
Forfeited-Number of options (in shares)	(9,725)	(12,650)
Outstanding ending-Number of options (in shares)	78,225	84,575
Exercisable-Number of options (in shares)	23,100	30,375
Outstanding-Weighted average exercise price (in dollars per share)	$ 24.33	$ 23.27
Granted-Weighted average exercise price (in dollars per share)	30.40	29.25
Exercised-Weighted average exercise price (in dollars per share)	20.70	17.81
Forfeited-Weighted average exercise price (in dollars per share)	25.61	31.87
Outstanding ending-Weighted average exercise price (in dollars per share)	26.85	24.25
Exercisable-Weighted average exercise price (in dollars per share)	$ 22.38	$ 20.87
Outstanding ending-Weighted average remaining contractual term	2 years 8 months 27 days	2 years 6 months
Exercisable-Weighted average remaining contractual term	10 months 13 days	10 months 21 days
Outstanding ending-Aggregate intrinsic value	$ 560	$ 444
Exercisable-Aggregate intrinsic value	$ 268	$ 262