Note 10 - Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2015

Note 10 - Stockholders' Equity (Tables) [Line Items]

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Year Ended December 31,
	2015				2014			2013
Risk-free interest rate	1.57	to	2.93%	%	2.31	to	2.75%	0.85	to	1.19%
Expected volatility	92.9	-	104.1%	%	94.3	-	100.7%	83.4	-	97.9%
Expected life (in years)		10				10		5.25	to	6.00
Expected forfeiture rate		5%				5%		5.0	to	7.5%
Expected dividend yield		0.0%				0.0%			0.0%

Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]

Shares of common stock associated with the Waived Warrants	Expiration Date of Waived Warrants	Strike Price		Per Share Fair Value on June 3, 2013		Per Share Fair Value on October 28, 2013
1,323,496	2/26/2018	$	5.31	$	6.60	$	3.86
31,243	7/25/2016	$	18.99	$	4.41	$	2.10
12,628	7/6/2016	$	14.09	$	4.81	$	2.40
31,448	11/25/2017	$	12.47	$	5.56	$	3.16

Prefered Stock [Member]

Note 10 - Stockholders' Equity (Tables) [Line Items]

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

Risk-free interest rate	0.78	%
Expected volatility	102.23	%
Expected life (in years)	5.0
Expected forfeiture rate	0.0	%
Expected dividend yield	0.0	%

Common Stock Offering [Member]

Note 10 - Stockholders' Equity (Tables) [Line Items]

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	June 3, 2013			October 28, 2013
Risk-free interest rate	0.50	-	1.03%	0.59	-	1.31%
Expected volatility	102.9	-	110.9%	105.1	-	111.8%
Expected life (in years)	3.1	-	4.7%	2.7	-	4.3%
Expected forfeiture rate		0.0%			0.0%
Expected dividend yield		0.00%			0.00%