Common Stock Warrants - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended		144 Months Ended						1 Months Ended	3 Months Ended	6 Months Ended			1 Months Ended		3 Months Ended		6 Months Ended		1 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Mar. 28, 2012	Mar. 22, 2012	Jun. 30, 2010	May 31, 2010	Apr. 30, 2009	Mar. 28, 2012 Warrant two	Jun. 30, 2011 Warrant two	Jun. 30, 2011 Warrant two	Jun. 30, 2011 Warrant two Minimum	Jun. 30, 2011 Warrant two Maximum	Mar. 28, 2012 Warrant one	Apr. 30, 2009 Warrant one	Jun. 30, 2012 Warrant one	Jun. 30, 2011 Warrant one	Jun. 30, 2012 Warrant one	Jun. 30, 2011 Warrant one	Mar. 07, 2011 Warrant three	Jun. 30, 2010 Warrant three	Jun. 30, 2011 Warrant three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants to purchase shares of common stock						1,333,361		100,000	12,000	33,333	46,378					1,333,361
Exercise price of warrant							5.63	4.26	15.00	3.00	5.63
Value of warrants			$ 10,000								$ 143,000					$ 4,445,000
Expected life			5 years 7 months 6 days	5 years 1 month 6 days	5 years 1 month 6 days									2 years 11 months 27 days	3 years 3 months 26 days		9 months 15 days					4 years 3 months 11 days
Expected volatility of the underlying stock			116.00%	121.00%	119.00%															78.00%		135.00%
Risk free interest			0.91%	1.91%	1.98%															0.21%		1.705%
Expected dividend rate			0.00%	0.00%	0.00%								0.00%							0.00%		0.00%
Number of warrant exercised																				33,333
Reversal of previously recognized expense																		45,000		88,000
Stock-based compensation expense	$ 879,000	$ 1,328,000	$ 1,352,000	$ 2,039,000	$ 10,934,000							$ 5,000	$ 12,000						$ 12,000		$ 20,000			$ 127,000
Volatility rate, minimum													128.00%
Volatility rate, maximum													130.00%
Risk free interest, minimum													0.79%
Risk free interest, Maximum													1.29%
Vested warrant													45,000										25,000
Forfeited warrant			616,726										27,000
Warrant expected to vest in one year																							25,000
Warrant that will vest upon the achievement of certain milestones																							50,000