Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2016

Fair Value Disclosures [Abstract]

Fair value of financial assets by level

The following table sets forth the fair value of our financial assets by level within the fair value hierarchy (in thousands):

	June 30, 2016
	Level I		Level II		Level III		Total
Financial Assets:
Money market funds	$	311,311	$	—	$	—	$	311,311
Money market funds-restricted	4,041		—		—		4,041
Commercial Paper	17,975		—		—		17,975
U.S. government notes	125,424		—		—		125,424
Corporate bonds	—		149,361		—		149,361
Total financial assets	$	458,751	$	149,361	$	—	$	608,112

	December 31, 2015
	Level I		Level II		Level III		Total
Financial Assets:
Money market funds	$	104,156	$	—	$	—	$	104,156
Money market funds-restricted	4,041		—		—		4,041
Total financial assets	$	108,197	$	—	$	—	$	108,197