Common Stock Warrants - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended		9 Months Ended		147 Months Ended					9 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended			1 Months Ended		9 Months Ended
	May 31, 2010	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Mar. 28, 2012	Mar. 22, 2012	Aug. 31, 2010	Apr. 30, 2009	Sep. 30, 2011 Warrant two	Mar. 28, 2012 Warrant two	Sep. 30, 2011 Warrant two Minimum	Sep. 30, 2011 Warrant two Maximum	Sep. 30, 2012 Warrant one	Sep. 30, 2011 Warrant one	Sep. 30, 2012 Warrant one	Sep. 30, 2011 Warrant one	Mar. 28, 2012 Warrant one	Mar. 07, 2011 Warrant three	Aug. 31, 2010 Warrant three	Sep. 30, 2011 Warrant three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants to purchase shares of common stock	12,000						1,333,361		100,000	33,333		46,378							1,333,361
Exercise price of warrant	15.00							5.63	4.26	3.00		5.63
Reversal of previously recognized expense															$ 10,000	$ 36,000	$ 98,000	$ 16,000
Vested warrant	7,500																				25,000
Forfeited warrant	4,500			616,726
Expected life				5 years 4 months 24 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						4 years 3 months 11 days
Volatility rate, minimum											128.00%
Volatility rate, maximum											130.00%
Risk free interest, minimum											0.79%
Risk free interest, Maximum											1.29%
Expected dividend rate				0.00%	0.00%	0.00%					0.00%									0.00%
Stock-based compensation expense		$ 819,000	$ 649,000	$ 2,170,000	$ 2,688,000	$ 11,752,000					$ 12,000											$ 340,000
Warrant expected to vest in one year																					25,000
Warrant that will vest upon the achievement of certain milestones																					50,000
Volatility rate				117.00%	121.00%	119.00%														135.00%
Risk free interest				0.84%	1.91%	1.87%														1.705%