Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2020

Financial Instruments

Schedule of available-for-sale securities

	September 30, 2020								December 31, 2019
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Estimated Fair Value		Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Estimated Fair Value
	(in thousands)
Money market deposits	$	178,894	$	—	$	—	$	178,894	$	22,477	$	—	$	—	$	22,477
U.S. Treasury securities (1)		526,643		4,173		(8)		530,808		292,506		731		(80)		293,157
Municipal securities		68,411		997		(11)		69,397		85,638		277		(7)		85,908
Total	$	773,948	$	5,170	$	(19)	$	779,099	$	400,621	$	1,008	$	(87)	$	401,542
Classified as:
Cash equivalents (2)							$	178,894							$	22,477
Short-term investments								600,205								379,065
Total							$	779,099							$	401,542

Summarized portfolio of available-for-sale securities by contractual maturity

	September 30, 2020
	Amortized Cost		Fair Value
	(in thousands)
Less than or equal to one year	$	338,583	$	339,655
Greater than one year but less than five years		256,464		260,550
Total	$	595,047	$	600,205