Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2012

Financial Instruments Measured at Fair Value on Recurring Basis by Level within Fair Value Hierarchy

The following table presents the Company’s financial instruments that were measured at fair value on a recurring basis as of December 31, 2012 by level within the fair value hierarchy (in thousands):

	December 31, 2012
	Level 1		Level 2		Level 3		Total
Financial Assets
Cash equivalents	$	25,781	$	2,829	$	—	$	28,610
Marketable securities—available-for-sale		1,997		116,190		—		118,187
Total	$	27,778	$	119,019	$	—	$	146,797
Financial Liability								—
Warrant liability	$	—	$	—	$	835	$	835

              The following table presents the Company’s financial instruments that were measured at fair value on a recurring basis as of December 31, 2011 by level within the fair value hierarchy (in thousands):

	December 31, 2011
	Level 1		Level 2		Level 3		Total
Financial Assets
Cash equivalents	$	17,160	$	6,145	$	—	$	23,305
Marketable securities—available-for-sale		7,023		207,921		—		214,944
Total	$	24,183	$	214,066	$	—	$	238,249

Change in Value of Warrant Liability

The change in the value of the warrant liability is summarized below (in thousands):

Fair value at December 31, 2011	$	—
Fair value of warrant on measurement date		7,705
Change in fair value recorded as a gain from change in fair value of warrant liability		(2,284	)
Reclassification to additional paid-in capital upon vesting of warrants		(4,586	)
Fair value at December 31, 2012	$	835

The change in the value of the warrant liability is summarized below (in thousands):

Fair value at December 31, 2010	$	2,961
Change in fair value recorded as a loss from change in fair value of warrant liability		3,637
Conversion of preferred stock warrants to common stock or common stock warrants		(6,598	)
Fair value at December 31, 2011	$	—