Note 5 - Stockholders' Equity - Summary of Restricted Stock Unit Activity (Details)	12 Months Ended
	Dec. 31, 2016 $ / shares shares
Outstanding (in shares) | shares	11,615
Outstanding, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 27.69
Granted Number of Warrants (in shares) | shares
Granted Weighted-Average Exercise Price (in dollars per share) | $ / shares
Exercised Number of Warrants (in shares) | shares	(4,250)
Exercised and converted to common shares, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 22.96
Forfeited Number of Warrants (in shares) | shares	(502)
Forfeited Weighted-Average Exercise Price (in dollars per share) | $ / shares	$ 26.26
Outstanding (in shares) | shares	6,863
Outstanding, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 30.70
Exercisable (in shares) | shares	6,863
Exercisable, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 30.70