Convertible Preferred Stock (Parenthetical) (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Class of Stock [Line Items]
Preferred stock, par value	$ 0.01	$ 0.01
Total preferred stock shares authorized for issuance	61,617,516	61,617,516
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized	17,006,275	17,006,275
Convertible Preferred Stock Issued	16,501,612	16,317,747
Preferred stock, shares outstanding	16,501,612	16,317,747
Preferred stock, aggregate liquidation preference	$ 17,574	$ 17,371
Series B Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized	16,410,526	16,410,526
Convertible Preferred Stock Issued	16,394,325	16,394,324
Preferred stock, shares outstanding	16,394,325	16,394,324
Preferred stock, aggregate liquidation preference	12,280	12,167
Series C Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized	15,621,609	15,621,609
Convertible Preferred Stock Issued	15,621,609	15,621,609
Preferred stock, shares outstanding	15,621,609	15,621,609
Preferred stock, aggregate liquidation preference	24,490	24,490
Series D Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized	9,007,678	9,007,678
Convertible Preferred Stock Issued	9,007,678	9,007,678
Preferred stock, shares outstanding	9,007,678	9,007,678
Preferred stock, aggregate liquidation preference	32,044	32,044
Series E Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized	3,571,428	3,571,428
Convertible Preferred Stock Issued	2,500,000	2,500,000
Preferred stock, shares outstanding	2,500,000	2,500,000
Preferred stock, aggregate liquidation preference	$ 17,500	$ 17,500