Note 13 - Warrants (Tables)

12 Months Ended

Dec. 31, 2015

Warrants [Abstract]

Schedule of Warrant Activity [Table Text Block]

Warrants	Number of Warrants Issued			Weighted Average Exercise Price
Warrants outstanding at January 1, 2013		1,747,478		$	15.17
Warrants issued in connection with 2013 equity transactions		1,341,382			5.31
Warrants issued in connection with the Hercules Credit Agreement (November 2013 tranche) as more fully described in Note 8		97,493			3.59
Warrants exercised for common stock in 2013		(15,833	)		14.63
Warrants outstanding at December 31, 2013		3,170,520		$	10.65
Warrants issued in connection with the January 2014 equity transaction		1,801,802			4.10
Warrants issued in connection with the Hercules Credit Agreement (June 2014 tranche) as more fully described in Note 8		97,493			3.59
Warrants outstanding at December 31, 2014		5,069,815		$	8.18
Warrants issued in connection with the May 2015 equity transaction		1,950,000		$	2.60
Warrants expired during 2015		(1,125,140	)	$	7.98
Warrants outstanding at December 31, 2015		5,894,675		$	6.37
Aggregate intrinsic value of outstanding warrants at December 31, 2015	$	–
Weighted average remaining contractual terms (years)		2.4

Schedule of Common Stock Warrant Liability Valuation Assumptions [Table Text Block]

	December 31,
	2014			2013
Risk-free interest rate	0.04	-	1.66%		0.13	%
Expected volatility	40.9	-	98.35%		64.74	%
Expected life (in years)	0.25	-	3.9		1.25
Expected forfeiture rate		0.0%			0.0	%
Expected dividend yield		0.00%			0.00	%

Schedule of Common Stock Warranty Liability [Table Text Block]

Balance at January 1, 2013	$	4,283,932
Fair value of warrants classified as liability (see Note 10)		9,110,302
Fair value of warrants classified as equity (see Note 10)		(5,300,572	)
Gain from the adjustment for the change in fair value included in net loss		(8,090,636	)
Ending balance, December 31, 2013	$	3,026
Fair value of warrants classified as liability (see Note 8)		476,261
Gain from the adjustment for the change in fair value included in net income		(204,279	)
Ending balance, December 31, 2014	$	275,008
Loss from the adjustment for the change in fair value included in net loss		61,246
Fair value of warrants reclassified as equity (Note 9)		(336,254	)
Ending balance as of December 31, 2015	$	–