Preferred Stock Warrant Liability - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended					12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Class of Warrant or Right [Line Items]
Conversion of convertible preferred stock warrants to common stock and common stock warrants							$ 6,598
Loss from change in fair value of warrant liability	$ (748)	$ (685)	$ (851)	$ 3,154	$ 483	$ (2,284)	$ 3,637	$ 2,638