Note 11 - Warrants (Tables)

12 Months Ended

Dec. 31, 2013

Warrants [Abstract]

Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]

Warrants	Number of Warrants Issued			Weighted Average Exercise Price
Warrants outstanding at January 1, 2011		224,239		$	23.58
Warrants issued in connection with 2011 equity transactions		2,394,398			13.28
Warrants exercised for common stock warrants in 2011		(34,859	)		12.29
Warrants outstanding at December 31, 2011		2,583,778		$	14,18
Warrants issued in connection with the Oxford & Horizon Credit Agreement as more fully described in Note 7		11,415		$	13.14
Warrants exercised for common stock in 2012		(847,715	)		12.11
Warrants outstanding at December 31, 2012		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 as more fully described in Note 7		194,986			3.59
Warrants exercised for common stock in 2013		(15,833	)		14.63
		3,268,013		$	10.43
Aggregate intrinsic value of outstanding warrants at December 31, 2013	$	58,496
Weighted average remaining contractual terms (years)		3.56

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

	December 31,
	2013			2012			2011
Risk-free interest rate		0.13	%		0.73	%		0.83	%
Expected volatility		64.74	%		92.02	%		75.17	%
Expected life (in years)		1.25			1.13			1.6
Expected forfeiture rate		0.0	%		0.0	%		0.0	%
Expected dividend yield		0.00	%		0.00	%		0.00	%

Schedule of Common Stock Warranty Liability [Table Text Block]

Beginning balance, January 1, 2011	$	248,131
Benefit from the adjustment for the change in fair value included in net loss for 2010		(81,733	)
Balance at December 31, 2011		166,398
Benefit from the adjustment for the change in fair value included in net loss for 2011		4,117,534
Balance at December 31, 2012		4,283,932
Fair value of warrants classified as liability (see Note 9)		9,110,302
Fair value of warrants classified as equity (see Note 9)		(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