Investments and Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2018

Investments and Fair Value Measurements

Schedule of available-for-sale securities

		December 31, 2018
				Gross		Gross
		Amortized		Unrealized		Unrealized		Estimated
(In thousands)		Cost		Gains		Losses		Fair Value
US government securities	Level 1	$	48,807	$	—	$	(86)	$	48,721
US government agency securities	Level 2		9,852		2		—		9,854
Corporate notes	Level 2		57,508		6		(88)		57,426
Commercial paper	Level 2		90,919		—		—		90,919
Marketable securities			207,086		8		(174)		206,920
Money market funds	Level 1		294,751		—		—		294,751
Total		$	501,837	$	8	$	(174)	$	501,671

		December 31, 2017
				Gross		Gross
		Amortized		Unrealized		Unrealized		Estimated
(In thousands)		Cost		Gains		Losses		Fair Value
US government securities	Level 1	$	89,896	$	—	$	(342)	$	89,554
US government agency securities	Level 2		50,891		—		(113)		50,778
Corporate notes	Level 2		141,226		2		(280)		140,948
Commercial paper	Level 2		19,893		—		—		19,893
Marketable securities			301,906		2		(735)		301,173
Money market funds	Level 1		69,055		—		—		69,055
Total		$	370,961	$	2	$	(735)	$	370,228