Stockholders Equity - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended		9 Months Ended			12 Months Ended		9 Months Ended	12 Months Ended	6 Months Ended	9 Months Ended		6 Months Ended	1 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 IPO	Mar. 19, 2013 IPO	Sep. 30, 2013 IPO Overallotment Option	Sep. 30, 2013 Stockholder Rights Plan	Sep. 30, 2013 Sales Agreement Mlv	Dec. 31, 2012 Sales Agreement Mlv	Sep. 30, 2013 Sales Agreement Mlv Maximum	Sep. 30, 2013 Sales Agreement Cantor	Dec. 31, 2012 Sales Agreement Cantor	Jun. 30, 2012 Series B Preferred Stock	Sep. 30, 2013 Series B Preferred Stock	Mar. 31, 1999 Series B Preferred Stock	Jun. 30, 2012 Common Stock	Aug. 31, 2009 Warrant 2009 Unit Offering	Nov. 30, 2010 Warrant 2010 Unit Offering	Sep. 30, 2013 Warrant 2010 Unit Offering
Stockholders Equity Note [Line Items]
Preferred stock issued																	3,327
Preferred stock conversion basis to common shares																100
Redeemable preferred stock, amount															$ 9,500,000
Conversion of preferred stock to Common stock															3,327
Common stock issued to Fresenius																		332,700
Conversion of preferred stock to common stock date																		Jun. 30, 2012
Warrants to purchase an aggregate shares of common stock																			2,400,000	3,700,000
Net proceeds from underwritten public offering																			12,100,000	19,700,000
Payment for underwriting discounts and commissions and stock issuance cost						500,000													1,100,000	1,300,000
Number of units sold in underwritten public offering																			6,000,000	7,400,000
Number of common stock in each unit																			1	1
Number of common stock shares purchasable with each warrant																			0.4	0.5
Units issues, price per unit																			$ 2.20
Common stock, number of shares issued										6,600,000			3,800,000	1,400,000					6,000,000	7,400,000
Warrant exercise price																			2.90	3.20
Exercisable period																			5 years	5 years
Warrant liability	22,706,000		22,706,000		5,903,000														2,800,000	5,800,000
Risk-free rate																			2.48%	1.23%
Expected term																			5 years	5 years
Dividend yield																			0.00%	0.00%
Volatility																			77.00%	85.00%
Units issued, price per unit																				$ 2.85
Warrants exercisable date																				May 15, 2011
Gain (Loss) from Revaluation of warrant liability	(12,416,000)	873,000	(16,803,000)	86,000
Warrants exercised																					5,084
Maximum common stock offering price											20,000,000			30,000,000
Percentage of proceeds payable as compensation to underwriter											3.00%			2.00%
Proceeds from common stock sold			50,981,000	10,823,000		38,000,000				19,200,000			13,000,000	4,300,000
Common stock available for sale												100,000	12,500,000
Common stock, number of shares issued						8,300,000		1,300,000
Common stock, price per share							$ 4.20
Gross proceeds from public offering						40,300,000
Underwriter's discount						$ 1,800,000
Minimum percentage of common stock acquired by stockholders									15.00%
Designated preferred stock for future issuance									250,000