Investments and Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2019

Investments and Fair Value Measurements

Schedule of available-for-sale securities

		September 30, 2019
				Gross		Gross
		Amortized		Unrealized		Unrealized		Estimated
(In thousands)		Cost		Gains		Losses		Fair Value
US government securities	Level 1	$	132,492	$	61	$	(15)	$	132,538
Corporate notes	Level 2		32,227		41		(1)		32,267
Commercial paper	Level 2		122,328		17		(7)		122,338
Marketable securities			287,047		119		(23)		287,143
Money market funds	Level 1		47,626		—		—		47,626
Total		$	334,673	$	119	$	(23)	$	334,769

		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