Note 10 - Stock Based Compensation - Summary of Stock Option Activity (Details) - Employee Stock Option [Member] - $ / shares	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Outstanding, beginning balance (in shares)	1,519,338
Outstanding, beginning balance, weighted average exercise price (in dollars per share)	$ 25.22
Granted (in shares)	39,037	0
Granted, weighted average exercise price (in dollars per share)	$ 54.15
Exercised (in shares)	(61,249)
Exercised, weighted average exercise price (in dollars per share)	$ 11.83
Outstanding, ending balance (in shares)	1,497,126
Outstanding, ending balance, weighted average exercise price (in dollars per share)	$ 26.52
Exercisable (in shares)	655,524
Exercisable, weighted average exercise price (in dollars per share)	$ 18.31