Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2021

Financial Instruments

Schedule of available-for-sale securities

	June 30, 2021								December 31, 2020
	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	$	5,509	$	—	$	—	$	5,509	$	28,990	$	—	$	—	$	28,990
U.S. Treasury securities (1)		432,610		2,180		(151)		434,639		594,252		3,512		(20)		597,744
Corporate bonds and notes (1)		14,284		2		(38)		14,248		12,331		2		(5)		12,328
Municipal securities		68,097		505		(57)		68,545		77,764		796		(26)		78,534
Total	$	520,500	$	2,687	$	(246)	$	522,941	$	713,337	$	4,310	$	(51)	$	717,596
Classified as:
Cash equivalents (2)							$	5,509							$	28,990
Short-term investments								517,432								688,606
Total							$	522,941							$	717,596

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

	June 30, 2021
	Amortized Cost		Fair Value
	(in thousands)
Less than or equal to one year	$	213,114	$	213,493
Greater than one year but less than five years		301,877		303,939
Total	$	514,991	$	517,432