Outstanding Series-A1 and Series-A2 Convertible Redeemable Preferred Stock, and Series A3 Convertible Preferred stock (Detail)	9 Months Ended
	Sep. 30, 2012
Class of Stock [Line Items]
Conversion of preferred stock	21,840,128
Redeemable Convertible Preferred Stock | Series A-1 convertible redeemable preferred stock
Class of Stock [Line Items]
Conversion of preferred stock	16,439,480
Redeemable Convertible Preferred Stock | Series A-2 convertible redeemable preferred stock
Class of Stock [Line Items]
Conversion of preferred stock	3,078,432
Convertible Redeemable Preferred Stock | Series A Three Preferred Stock
Class of Stock [Line Items]
Conversion of preferred stock	2,322,216