Preferred Stock Warrant Liabilities - Additional Information (Detail) (USD $)					1 Months Ended		9 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Loan and Security Agreement	Sep. 30, 2012 Loan and Security Agreement	Oct. 31, 2005 Series B-2 Preferred Stock	Dec. 31, 2006 Series B-2 Preferred Stock	Sep. 30, 2012 Series E Preferred Stock Loan and Security Agreement	Dec. 31, 2012 Series E Preferred Stock Loan and Security Agreement
Class of Warrant or Right [Line Items]
Preferred Stock, issued per share amount			$ 12.11	$ 12.11	$ 5.13
Warrant, expiration date					Oct. 31, 2015		Feb. 28, 2013	Feb. 28, 2013
Warrant to purchase shares of preferred stock					15,599	38,997	33,032	33,032
Warrant exercisable in common stock per share	$ 0.001	$ 0.001			$ 5.13
Warrants issued as Percentage of Amount drawn under credit facility			4.00%	4.00%