Note 10 - Summary of Stock Option Activity (Details) - Employee Stock Option [Member]	3 Months Ended
	Mar. 31, 2016 $ / shares shares
Outstanding, beginning balance (in shares) | shares	1,631,913
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 19.17
Exercised (in shares) | shares	(44,279)
Exercised (in dollars per share) | $ / shares	$ 9.47
Forfeited or expired (in shares) | shares	(5,250)
Forfeited or expired (in dollars per share) | $ / shares	$ 16.45
Outstanding, ending balance (in shares) | shares	1,582,384
Outstanding, ending balance (in dollars per share) | $ / shares	$ 19.45
Exercisable at March 31, 2016 (in shares) | shares	679,851
Exercisable at March 31, 2016 (in dollars per share) | $ / shares	$ 12.65