Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Measurements

Schedule of assets measured at fair value on a recurring basis

Assets measured at fair value on a recurring basis are summarized below (in thousands):

	Fair Value Measurements as of September 30, 2018
	Total		Level 1		Level 2		Level 3
Cash, Cash Equivalents	$	324,561	$	324,561	$	—	$	—
Marketable Securities
Bonds and bond funds	$	159,942	$	—	$	159,942	$	—
Commercial paper		220,300		—		220,300		—
		380,242		—		380,242		—
Total Assets Measured at Fair Value	$	704,803	$	324,561	$	380,242	$	—

	Fair Value Measurements as of December 31, 2017
	Total		Level 1		Level 2		Level 3
Cash, Cash Equivalents	$	181,792	$	181,792	$	—	$	—
Marketable Securities
Bonds and bond funds	$	344,251	$	—	$	344,251	$	—
Commercial paper		159,252		—		159,252		—
		503,503		—		503,503		—
Total Assets Measured at Fair Value	$	685,295	$	181,792	$	503,503	$	—