Note 4 - Stockholders' Equity - Outstanding Options Granted to Consultants for Sales and Pre-Marketing Services (Details)	9 Months Ended
	Sep. 30, 2015 $ / shares shares
February 2013 [Member] | Consultants [Member]
Options for shares of common stock (in shares)	3,500
Exercise price per share (in dollars per share) | $ / shares	$ 12.47
Options exercisable (in shares)	2,083
Exercisable through	February 2023
August 2013 [Member] | Consultants [Member]
Options for shares of common stock (in shares)	5,000
Exercise price per share (in dollars per share) | $ / shares	$ 21.14
Options exercisable (in shares)	2,510
Exercisable through	August 2023
October 2013 [Member] | Consultants [Member]
Options for shares of common stock (in shares)	1,084
Exercise price per share (in dollars per share) | $ / shares	$ 24.23
Options exercisable (in shares)	433
Exercisable through	October 2023
March 2014 [Member] | Consultants [Member]
Options for shares of common stock (in shares)	14,917
Exercise price per share (in dollars per share) | $ / shares	$ 39.86
Options exercisable (in shares)	5,698
Exercisable through	March 2024
May 2014 [Member] | Consultants [Member]
Options for shares of common stock (in shares)	8,700
Exercise price per share (in dollars per share) | $ / shares	$ 22.01
Options exercisable (in shares)	2,900
Exercisable through	May 2024
August 2014 [Member] | Consultants [Member]
Options for shares of common stock (in shares)	1,250
Exercise price per share (in dollars per share) | $ / shares	$ 21
Options exercisable (in shares)	339
Exercisable through	August 2024
November 2014 [Member] | Consultants [Member]
Options for shares of common stock (in shares)	12,000
Exercise price per share (in dollars per share) | $ / shares	$ 21.66
Exercisable through	November 2024
May 2015 [Member] | Consultants [Member]
Options for shares of common stock (in shares)	6,250
Exercise price per share (in dollars per share) | $ / shares	$ 19.51
Exercisable through	May 2025
Consultants [Member]
Options for shares of common stock (in shares)	52,701
Options exercisable (in shares)	13,963
Exercise price per share (in dollars per share) | $ / shares	$ 28.253
Options exercisable (in shares)	1,954,109