Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2015

Fair Value Disclosures [Abstract]

Schedule of Fair Value of Financial Assets and Liabilities Measured on Recurring Basis

The following table sets forth the fair value of the Company’s financial assets and liabilities measured at fair value on a recurring basis based on the three-tier fair value hierarchy (in thousands):

	March 31, 2015
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	117,556	$	—	$	—	$	117,556
Commerical paper		—		44,540		—		44,540
U.S. government and agency securities		—		203,809		—		203,809
Corporate debt securities		—		75,194		—		75,194
Total financial assets	$	117,556	$	323,543	$	—	$	441,099
Financial Liabilities:
Fair value of success payments liabilities attributable to the elapsed service period	$	—	$	—	$	123,830	$	123,830
Total financial liabilities	$	—	$	—	$	123,830	$	123,830

	December 31, 2014
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	223,745	$	—	$	—	$	223,745
Commerical paper		—		15,293		—		15,293
U.S. government and agency securities		—		90,302		—		90,302
Corporate debt securities		—		35,066		—		35,066
Total financial assets	$	223,745	$	140,661	$	—	$	364,406
Financial Liabilities:
Fair value of success payments liabilities attributable to the elapsed service period	$	—	$	—	$	84,920	$	84,920
Total financial liabilities	$	—	$	—	$	84,920	$	84,920

Summary of Changes in Fair Value of Level 3 Financial Liabilities

The following table sets forth a summary of the changes in the fair value of the Company’s Level 3 financial liabilities (in thousands):

Balance at December 31, 2014	$	84,920
Change in fair value of success payments liabilities attributable to the elapsed service period recorded in research and development expense		38,910
Balance at March 31, 2015	$	123,830