Stockholders Equity - Additional Information (Detail) (USD $)	12 Months Ended					6 Months Ended	12 Months Ended		6 Months Ended	1 Months Ended		6 Months Ended	12 Months Ended			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2010 Maximum	Dec. 31, 2012 Stockholder Rights Plan	Jun. 30, 2012 Series B Convertible Preferred Stock	Dec. 31, 2012 Series B Convertible Preferred Stock	Mar. 31, 1999 Series B Convertible Preferred Stock	Jun. 30, 2012 Common Stock	Aug. 31, 2009 Warrant 2009 Unit Offering	Nov. 30, 2010 Warrant 2010 Unit Offering	Jun. 30, 2012 Warrant 2010 Unit Offering	Dec. 31, 2012 Sales Agreement Mlv	Dec. 31, 2011 Sales Agreement Mlv	Dec. 31, 2012 Sales Agreement Mlv Maximum	Dec. 31, 2012 Sales Agreement Cantor
Stockholders Equity Note [Line Items]
Preferred stock issued	0	3,000						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
warrant exercise price										2.90	3.20
Exercisable period										5 years	5 years
Warrant liability	5,903,000	7,979,000								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%
Net proceeds from underwritten public offering											19,700,000
Payment for underwriting discounts and commissions and stock issuance cost	550,000	420,000	1,710,000								1,300,000
Number of units sold in underwritten public offering											7,400,000
Number of common stock in each unit											1
Number of common stock shares purchasable with each warrant											0.5
Units issues, price per unit											$ 2.85
Common stock, number of shares issued											7,400,000
Warrants, number of common stock shares											3,700,000
Warrants exercisable date											May 15, 2011
Revaluation of warrant liability	2,059,000	486,000	39,000	100,000
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%
Common stock, sold													3,100,000	3,500,000		1,400,000
Proceeds from common stock sold	$ 14,226,000	$ 9,273,000	$ 19,291,000										$ 9,500,000	$ 9,700,000		$ 4,300,000
Common stock available to be sold															100,000	25,500,000
Minimum percentage of common stock acquired by stockholders					15.00%
Designated preferred stock for future issuance					250,000