Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2020

Financial Instruments

Schedule of available-for-sale securities

	June 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	$	28,795	$	—	$	—	$	28,795	$	22,477	$	—	$	—	$	22,477
U.S. Treasury securities (1)		399,622		4,820		(26)		404,416		292,506		731		(80)		293,157
Municipal securities		88,460		981		(5)		89,436		85,638		277		(7)		85,908
Total	$	516,877	$	5,801	$	(31)	$	522,647	$	400,621	$	1,008	$	(87)	$	401,542
Classified as:						—
Cash equivalents (2)							$	28,795							$	22,477
Short-term investments								493,852								379,065
Total							$	522,647							$	401,542

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

	June 30, 2020
	Amortized Cost		Fair Value
(in thousands)
Less than one year	$	264,713	$	265,534
Greater than one year but less than five years		223,369		228,318
Total	$	488,082	$	493,852