Summary of Preferred Stock Terms (Parenthetical) (Detail) (USD $)	6 Months Ended
	Jun. 30, 2012
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock, liquidation Value per share	$ 4.50
Series B Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock, liquidation Value per share	$ 4.00
Preferred stock, frequency of dividend payment	Quarterly
Preferred stock, dividend date of commencement	Mar. 31, 2001
Series C Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock, liquidation Value per share	$ 3.00
Preferred stock, frequency of dividend payment	Quarterly
Preferred stock, dividend date of commencement	Mar. 31, 2002
Series D Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock, liquidation Value per share	$ 10.00
Preferred stock, frequency of dividend payment	Quarterly
Preferred stock, dividend date of commencement	Apr. 30, 2002
Series E Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock, liquidation Value per share	$ 22.00
Preferred stock, frequency of dividend payment	Quarterly
Preferred stock, dividend date of commencement	May 31, 2002