Investments and Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Investments and Fair Value Measurements

Schedule of available-for-sale securities

		December 31, 2019
				Gross		Gross
		Amortized		Unrealized		Unrealized		Estimated
(In thousands)		Cost		Gains		Losses		Fair Value
US government securities	Level 1	$	100,746	$	108	$	—	$	100,854
US government agency securities	Level 2		—		—		—		—
Corporate notes	Level 2		25,466		9		(1)		25,474
Commercial paper	Level 2		112,066		31		(2)		112,095
Marketable securities			238,278		148		(3)		238,423
Money market funds	Level 1		35,736		—		—		35,736
Total		$	274,014	$	148	$	(3)	$	274,159

		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