Fair Value of Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2012

Fair Value of Financial Instruments

Schedule of assets and liabilities measured at fair value on a recurring basis

As of December 31, 2011 (in thousands)	Level 1		Level 2		Level 3
Assets:
Cash equivalents — money market funds	$	35,076	$	—	$	—
Liabilities:
Convertible preferred stock warrants	—		—		1,516

As of September 30, 2012 (in thousands)	Level 1		Level 2	Level 3
Assets:
Cash equivalents — money market funds	$	25,197	$	$
Investments — U.S. government agencies securities			1,000
Investments — corporate debt securities			57,759

Schedule of fair value of convertible preferred stock warrants categorized as Level 3 instruments

(in thousands)	Convertible preferred stock warrants
Balance, December 31, 2011	$	1,516
Unrealized gain included in other income (expense)	(587		)
Reclassification to common stock warrants	(929		)
Balance, September 30, 2012	$	—