Convertible Preferred Stock (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Convertible preferred stock:
Preferred stock	$ 103,219	$ 103,023
Series A Convertible Preferred Stock
Convertible preferred stock:
Preferred stock	17,376	17,181
Series B Convertible Preferred Stock
Convertible preferred stock:
Preferred stock	12,165	12,164
Series C Convertible Preferred Stock
Convertible preferred stock:
Preferred stock	24,388	24,388
Series D Convertible Preferred Stock
Convertible preferred stock:
Preferred stock	31,943	31,943
Series E Convertible Preferred Stock
Convertible preferred stock:
Preferred stock	$ 17,347	$ 17,347