Investments

6 Months Ended

Jun. 30, 2023

Schedule of Investments [Abstract]

Investments

4. Investments

The fair value of available-for-sale investments by type of security was as follows:

	June 30, 2023
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
Investments:
U.S. treasury bills	$	238,934	$	—	$	(2,343	)	$	236,591
U.S. agency securities		340,204		—		(2,586	)		337,618
Total investments with a maturity of one year or less		579,138		—		(4,929	)		574,209
U.S. treasury bills		142,850		—		(1,050	)		141,800
U.S. agency securities		9,764		—		(102	)		9,662
Total investments with a maturity of one to two years		152,614		—		(1,152	)		151,462
Total investments	$	731,752	$	—	$	(6,081	)	$	725,671

	December 31, 2022
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
Investments:
U.S. treasury bills	$	356,728	$	9	$	(5,523	)	$	351,214
U.S. agency securities		236,483		49		(3,104	)		233,428
Total investments with a maturity of one year or less		593,211		58		(8,627	)		584,642
U.S. treasury bills		116,290		14		(915	)		115,389
U.S. agency securities		148,042		36		(986	)		147,092
Total investments with a maturity of one to two years		264,332		50		(1,901	)		262,481
Total investments	$	857,543	$	108	$	(10,528	)	$	847,123

The following tables summarize the Company's available-for-sale debt securities in an unrealized loss position for which an allowance for credit losses has not been recorded, aggregated by major security type and length of time in a continuous unrealized loss position:

	June 30, 2023
	Less than 12 Months					12 Months or Longer					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	(in thousands)
U.S. treasury bills	$	225,573	$	(1,528	)	$	152,818	$	(1,864	)	$	378,391	$	(3,392	)
U.S. agency securities		258,424		(1,213	)		88,856		(1,476	)		347,280		(2,689	)
Total	$	483,997	$	(2,741	)	$	241,674	$	(3,340	)	$	725,671	$	(6,081	)

	December 31, 2022
	Less than 12 Months					12 Months or Longer					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	(in thousands)
U.S. treasury bills	$	143,089	$	(1,860	)	$	275,445	$	(4,578	)	$	418,534	$	(6,438	)
U.S. agency securities		190,468		(1,649	)		97,305		(2,441	)		287,773		(4,090	)
Total	$	333,557	$	(3,509	)	$	372,750	$	(7,019	)	$	706,307	$	(10,528	)

As summarized in the tables immediately above, the Company held 142 and 126 debt securities that were in an unrealized loss position as of June 30, 2023 and December 31, 2022, respectively. The unrealized losses at June 30, 2023 and December 31, 2022 were attributable to changes in interest rates and the unrealized losses do not represent credit losses. The Company does not intend to sell these securities and it is not more likely than not that it will be required to sell them before recovery of their amortized cost basis.