The amortized cost, gross unrealized holding gains, gross unrealized holding losses and fair value of debt securities available-for-sale by type of security at September 30, 2024 and December 31, 2023 were as follows:


	Amortized Cost		Allowance for Credit Losses		Net Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
September 30, 2024
Debt securities



U.S. treasury bills	$	294,211	$	—	$	294,211	$	215	$	—	$	294,426



December 31, 2023
Debt securities
U.S. corporate bonds	$	46,228	$	—	$	46,228	$	7	$	(24)	$	46,211
Foreign corporate bonds	7,180		—		7,180		—		(7)		7,173

U.S. treasury bills	113,908		—		113,908		27		—		113,935

Total	$	167,316	$	—	$	167,316	$	34	$	(31)	$	167,319

The fair value of debt securities available-for-sale by classification in the condensed consolidated balance sheets was as follows:


	September 30, 2024		December 31, 2023
Cash and cash equivalents	$	—	$	33,902
Marketable securities	294,426		133,417
Total	$	294,426	$	167,319

The net amortized cost and fair value of debt securities available-for-sale at September 30, 2024 and December 31, 2023 are shown below by contractual maturity. Actual maturities may differ from contractual maturities because securities may be restructured, called or prepaid, or the Company intends to sell a security prior to maturity.


	September 30, 2024				December 31, 2023
	Net Amortized Cost		Fair Value		Net Amortized Cost		Fair Value
Due to mature:
Less than one year	$	294,211	$	294,426	$	167,316	$	167,319

The Company did not hold any debt securities available-for-sale that were in an unrealized loss position at September 30, 2024. Summarized below are the debt securities available-for-sale the Company held at December 31, 2023 that were in an unrealized loss position, aggregated by the length of time the investments have been in that position:


	Less than 12 months
	Number of Securities	Fair Value		Unrealized Losses








December 31, 2023
Debt securities
U.S. corporate bonds	6	$	29,537	$	(24)
Foreign corporate bonds	1	7,173		(7)



Total	7	$	36,710	$	(31)

The Company did not have any investments in a continuous unrealized loss position for more than twelve months as of September 30, 2024 or December 31, 2023.

The Company reviewed its securities and concluded that they are performing assets, considering factors such as the credit quality of the investment security based on research performed by external rating agencies and the prospects of realizing the carrying value of the security based on the investment’s current prospects for recovery. As of September 30, 2024, the Company did not intend to sell its securities and did not believe it was more likely than not that it would be required to sell its securities prior to the anticipated recovery of their amortized cost basis.

Gross investment income includes income from debt securities available-for-sale, money-market funds, cash and restricted cash. Net investment income included in other income, net in the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2024 and 2023 were as follows:


	Three Months Ended September 30,				Nine Months Ended September 30,
	2024		2023		2024		2023
Debt securities (including realized losses)	$	3,843	$	2,280	$	8,912	$	7,914
Other investments	1,850		1,551		6,252		4,278
Gross investment income (including realized losses)	5,693		3,831		15,164		12,192
Investment expenses	(45)		(65)		(115)		(203)
Net investment income	$	5,648	$	3,766	$	15,049	$	11,989

We utilize the specific identification method in computing realized gains and losses. There were no proceeds from the sale of available-for-sale debt securities or related gross realized capital gains or losses for the three months ended September 30, 2024 and 2023. The proceeds from the sale of available-for-sale debt securities and the related gross realized capital losses for the nine months ended September 30, 2024 and 2023 were as follows:


	Nine Months Ended September 30,
		2024		2023
Proceeds from sales		$	—	$	4,920

Gross realized capital losses		$	—	$	39