Note 4 - Outstanding Options Granted to Consultants for Sales and Pre-Marketing Services (Details)	6 Months Ended
	Jun. 30, 2016 $ / shares shares
Consultants [Member] | February 2013 [Member]
Options for shares of common stock (in shares)	3,000
Granted (in dollars per share) | $ / shares	$ 12.47
Options exercisable (in shares)	2,500
Exercisable through	February 2023
Consultants [Member] | August 2013 [Member]
Options for shares of common stock (in shares)	5,000
Granted (in dollars per share) | $ / shares	$ 21.14
Options exercisable (in shares)	3,542
Exercisable through	August 2023
Consultants [Member] | October 2013 [Member]
Options for shares of common stock (in shares)	750
Granted (in dollars per share) | $ / shares	$ 24.23
Options exercisable (in shares)	500
Exercisable through	October 2023
Consultants [Member] | March 2014 [Member]
Options for shares of common stock (in shares)	13,750
Granted (in dollars per share) | $ / shares	$ 39.86
Options exercisable (in shares)	7,734
Exercisable through	March 2024
Consultants [Member] | May 2014 [Member]
Options for shares of common stock (in shares)	8,700
Granted (in dollars per share) | $ / shares	$ 22.01
Options exercisable (in shares)	4,531
Exercisable through	May 2024
Consultants [Member] | November 2014 [Member]
Options for shares of common stock (in shares)	12,000
Granted (in dollars per share) | $ / shares	$ 21.66
Options exercisable (in shares)	4,750
Exercisable through	November 2024
Consultants [Member] | May 2015 [Member]
Options for shares of common stock (in shares)	5,250
Granted (in dollars per share) | $ / shares	$ 19.51
Options exercisable (in shares)	1,422
Exercisable through	May 2025
Consultants [Member] | February 2016 [Member]
Options for shares of common stock (in shares)	3,000
Granted (in dollars per share) | $ / shares	$ 16.87
Options exercisable (in shares)
Exercisable through	February 2026
Consultants [Member]
Options for shares of common stock (in shares)	51,450
Granted (in dollars per share) | $ / shares
Options exercisable (in shares)	24,979
Exercisable through
Granted (in dollars per share) | $ / shares	$ 16.87
Options exercisable (in shares)	1,879,372