Weighted-Average Assumptions (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Class of Warrant or Right [Line Items]
Expected dividend yield	0.00%		0.00%
Shares underlying warrants classified as liabilities	3,093,676		4,824,827
Market value of stock at beginning of year	$ 25.80		$ 4.50
Market value of stock at end of period	$ 36.95		$ 9.24
Minimum
Class of Warrant or Right [Line Items]
Risk-free interest rate	0.10%		0.20%
Expected lives	9 months 18 days		8 months 12 days
Expected volatility	99.40%	[1]	65.10%	[1]
Maximum
Class of Warrant or Right [Line Items]
Risk-free interest rate			0.30%
Expected lives	1 year 4 months 24 days		2 years 4 months 24 days
Expected volatility	110.70%	[1]	82.40%	[1]

[1] For the three month period ended March 31, 2013, expected volatility has been estimated using a blend of calculated volatility of the Company's common stock over a historical period and implied volatility in exchange-traded options associated with the Company's common stock. Prior to January 1, 2013, expected volatility has been estimated using calculated volatility of the Company's common stock over a historical period commensurate with the expected term of the option.