The Fair Value of the Warrants Determined Using the Black-Scholes Option Valuation Model (Detail) (Warrant Liability [Member], USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Warrant Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Market price per share of the Company's common stock	$ 12.25	$ 5.10	$ 2.28
Risk-free interest rate	0.015%	0.34%	1.23%
Expected term (years)	0.02	1.2	2.2
Dividend yield
Volatility	59.90%	54.00%	79.00%