Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Measurements

Schedule of assets measured at fair value on a recurring basis

As of December 31, 2018, the Company held certain assets that are required to be 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 December 31, 2018
	Total		Level 1		Level 2		Level 3
Marketable Securities
Bonds and bond funds	$	229,783	$	—	$	229,783	$	—
Commercial paper		131,162		—		131,162		—
	$	360,945	$	—	$	360,945	$	—
Cash, Cash Equivalents and Restricted Cash		328,384		328,384		—		—
Total Assets Measured at Fair Value	$	689,329	$	328,384	$	360,945	$	—

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