Note 6 - Stock-Based Compensation (Details) - Stock Option Activity (USD $)	3 Months Ended
	Mar. 31, 2014
Stock Option Activity [Abstract]
Options outstanding at December 31, 2013	1,143,250
Options outstanding at December 31, 2013	$ 19.03
Granted	69,350
Granted	$ 78.59
Exercised	(47,255)
Exercised	$ 14.06
Forfeited	(804)
Forfeited	$ 30.58
Options outstanding at March 31, 2014	1,164,541
Options outstanding at March 31, 2014	$ 22.77
Exercisable at March 31, 2014	434,412
Exercisable at March 31, 2014	$ 10.99