Stock Purchase Warrants - Additional Information (Detail) (USD $)			3 Months Ended		9 Months Ended
	Sep. 30, 2013 Convertible Preferred Stock Warrants [Member]	Dec. 31, 2012 Convertible Preferred Stock Warrants [Member]	Sep. 30, 2013 Other Income (Expense) [Member]	Sep. 30, 2012 Other Income (Expense) [Member]	Sep. 30, 2013 Other Income (Expense) [Member]	Sep. 30, 2012 Other Income (Expense) [Member]
Class of Warrant or Right [Line Items]
Number of shares of convertible preferred stock into which the warrants may be converted	6,388,431	2,979,345
Other income (expense), net			$ 3,500,000	$ 788,000	$ 3,800,000	$ 441,000