Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2021

Financial Instruments

Schedule of available-for-sale securities

	September 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	$	55,703	$	—	$	—	$	55,703	$	28,990	$	—	$	—	$	28,990
U.S. Treasury securities (1)		786,404		1,821		(350)		787,875		594,252		3,512		(20)		597,744
Corporate bonds and notes (1)		52,868		—		(147)		52,721		12,331		2		(5)		12,328
Municipal securities		87,824		378		(202)		88,000		77,764		796		(26)		78,534
Total	$	982,799	$	2,199	$	(699)	$	984,299	$	713,337	$	4,310	$	(51)	$	717,596
Classified as:
Cash equivalents (2)							$	55,703							$	28,990
Short-term investments								928,596								688,606
Total							$	984,299							$	717,596

(1) Per the Company’s investment policy, all debt securities are classified as short-term investments irrespective of holding period.  

(2) Cash equivalents includes cash sweep accounts and U.S. Treasury money market mutual funds.

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

	September 30, 2021
	Amortized Cost		Fair Value
	(in thousands)
Less than or equal to one year	$	403,211	$	403,784
Greater than one year but less than five years		523,885		524,812
Total	$	927,096	$	928,596