Note 11 - Shareholders' Equity - Reconciliation of Outstanding Stock Options (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares
Outstanding (in shares) | shares	470,904
Outstanding (in dollars per share) | $ / shares	$ 80.53
Granted (in shares) | shares	123,435
Granted (in dollars per share) | $ / shares	$ 120.15
Exercised (in shares) | shares	(229,319)
Exercised (in dollars per share) | $ / shares	$ 73.42
Forfeited (in shares) | shares	(8,836)
Forfeited (in dollars per share) | $ / shares	$ 87.86
Outstanding (in shares) | shares	356,184
Outstanding (in dollars per share) | $ / shares	$ 98.65
Outstanding (Year)	5 years
Outstanding | $	$ 18,920
Exercisable (in shares) | shares	112,714
Exercisable (in dollars per share) | $ / shares	$ 78.16
Exercisable (Year)	3 years 219 days
Exercisable | $	$ 8,297