Fair Value of Financial Instruments (Tables)

6 Months Ended

Jun. 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 — U.S. treasury securities	$	35,076	$	—	$	—
Liabilities:
Convertible preferred stock warrants	—		—		1,516

As of June 30, 2012 (in thousands)	Level 1		Level 2		Level 3
Assets:
Cash equivalents — money market funds	$	23,794	$	—	$	—
Cash equivalents — corporate debt securities	—		6,000		—
Investments — U.S. government agencies securities	—		999		—
Investments — corporate debt securities	—		73,670		—

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, June 30, 2012	$	—