Note 9 - Summary of Stock Option Activity (Details) - Employee Stock Option [Member] - $ / shares	3 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015
Outstanding (in shares)	1,768,714	1,807,521	2,070,672
Outstanding (in dollars per share)	$ 13.35	$ 12.72	$ 12.08
Granted (in shares)		23,818	29,500
Granted (in dollars per share)		$ 41.11	$ 23.45
Exercised (in shares)	(157,850)	(62,625)	(212,276)
Exercised (in dollars per share)	$ 6.74	$ 5.68	$ 7.25
Forfeited or expired (in shares)			(80,375)
Forfeited or expired (in dollars per share)			$ 14.48
Outstanding (in shares)	1,610,864	1,768,714	1,807,521
Outstanding (in dollars per share)	$ 14	$ 13.35	$ 12.72
Exercisable at September 30, 2015 (in shares)	577,796
Exercisable at September 30, 2015 (in dollars per share)	$ 10.16