Schedule of Weighted Average Key Assumptions Used in Determining Fair Value of Stock Option (Detail) (Stock Options, USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Stock Options
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Weighted-average volatility	107.40%	95.00%	106.90%	94.00%
Weighted-average risk-free interest rate	0.90%	0.80%	0.80%	1.00%
Weighted-average expected life in years	5 years	4 years 10 months 24 days	4 years 10 months 24 days	5 years 4 months 24 days
Dividend yield	0.00%	0.00%	0.00%	0.00%
Weighted-average grant date fair value per share	$ 0.56	$ 0.60	$ 0.73	$ 1.27