Note 4 - Stockholders' Equity - Outstanding Options Granted to Consultants for Sales and Pre-Marketing Services (Details)	9 Months Ended
	Sep. 30, 2016 $ / shares shares
Consultants [Member] | February 2013 [Member]
Options for shares of common stock (in shares)	1,500
Exercise price per share (in dollars per share) | $ / shares	$ 12.47
Options exercisable at the end of the year (in shares)	1,344
Exercisable through	February 2023
Consultants [Member] | August 2013 [Member]
Options for shares of common stock (in shares)	4,250
Exercise price per share (in dollars per share) | $ / shares	$ 21.14
Options exercisable at the end of the year (in shares)	3,104
Exercisable through	August 2023
Consultants [Member] | October 2013 [Member]
Options for shares of common stock (in shares)	750
Exercise price per share (in dollars per share) | $ / shares	$ 24.23
Options exercisable at the end of the year (in shares)	547
Exercisable through	October 2023
Consultants [Member] | March 2014 [Member]
Options for shares of common stock (in shares)	13,494
Exercise price per share (in dollars per share) | $ / shares	$ 39.86
Options exercisable at the end of the year (in shares)	8,581
Exercisable through	March 2024
Consultants [Member] | May 2014 [Member]
Options for shares of common stock (in shares)	6,912
Exercise price per share (in dollars per share) | $ / shares	$ 22.01
Options exercisable at the end of the year (in shares)	3,704
Exercisable through	May 2024
Consultants [Member] | November 2014 [Member]
Options for shares of common stock (in shares)	10,321
Exercise price per share (in dollars per share) | $ / shares	$ 21.66
Options exercisable at the end of the year (in shares)	4,364
Exercisable through	November 2024
Consultants [Member] | May 2015 [Member]
Options for shares of common stock (in shares)	5,250
Exercise price per share (in dollars per share) | $ / shares	$ 19.51
Options exercisable at the end of the year (in shares)	1,750
Exercisable through	May 2025
Consultants [Member] | February 2016 [Member]
Options for shares of common stock (in shares)	2,500
Exercise price per share (in dollars per share) | $ / shares	$ 16.87
Options exercisable at the end of the year (in shares)
Exercisable through	February 2026
Consultants [Member]
Options for shares of common stock (in shares)	44,977
Exercise price per share (in dollars per share) | $ / shares
Options exercisable at the end of the year (in shares)	23,394
Exercisable through
Exercise price per share (in dollars per share) | $ / shares	$ 16.87
Options exercisable at the end of the year (in shares)	1,784,407