Investments and Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2020

Investments and Fair Value Measurements

Schedule of available-for-sale securities

		June 30, 2020
				Gross		Gross
		Amortized		Unrealized		Unrealized		Estimated
(In thousands)		Cost		Gains		Losses		Fair Value
US government securities	Level 1	$	189,878	$	211	$	(2)	$	190,087
US government agency securities	Level 2		99,877		37		—		99,914
Corporate notes	Level 2		2,616		9		—		2,625
Commercial paper	Level 2		60,949		27		(2)		60,974
Marketable securities			353,320		284		(4)		353,600
Money market funds	Level 1		30,637		—		—		30,637
Total		$	383,957	$	284	$	(4)	$	384,237

		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
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

Schedule of Available for sale debt securities with unrealized losses

	June 30, 2020
	Less than 12 Months				Greater than 12 Months				Total
			Gross				Gross				Gross
	Estimated		Unrealized		Estimated		Unrealized		Estimated		Unrealized
(In thousands)	Fair Value		Losses		Fair Value		Losses		Fair Value		Losses
US government securities	$	49,974	$	(1)	$	—	$	—	$	49,974	$	(1)
Commercial paper		9,991		(2)		—		—		9,991		(2)
Total	$	59,965	$	(3)	$	—	$	—	$	59,965	$	(3)

	December 31, 2019
	Less than 12 Months				Greater than 12 Months				Total
			Gross				Gross				Gross
	Estimated		Unrealized		Estimated		Unrealized		Estimated		Unrealized
(In thousands)	Fair Value		Losses		Fair Value		Losses		Fair Value		Losses
Corporate notes	$	5,507	$	(1)	$	—	$	—	$	5,507	$	(1)
Commercial paper		28,137		(2)		—		—		28,137		(2)
Total	$	33,644	$	(3)	$	—	$	—	$	33,644	$	(3)