Weighted-Average Assumptions (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Class of Warrant or Right [Line Items]
Expected dividend yield	0.00%	0.00%	0.00%
Warrants classified as liabilities	3,127,618	4,824,827	4,901,591
Market value of stock at beginning of year	$ 4.50	$ 12.72	$ 8.76
Market value of stock at end of year	$ 25.80	$ 4.50	$ 12.72
Minimum
Class of Warrant or Right [Line Items]
Risk-free interest rate	0.20%	0.10%	0.60%
Expected lives	1 year 1 month 6 days	1 year	2 years
Expected volatility	139.20%	71.80%	84.70%
Maximum
Class of Warrant or Right [Line Items]
Risk-free interest rate	0.30%	0.40%	1.00%
Expected lives	1 year 7 months 6 days	2 years 8 months 12 days	3 years 8 months 12 days
Expected volatility	164.10%	75.60%	90.10%