We invest in available-for-sale securities consisting of money market funds, U.S. Treasury securities, corporate debt securities, commercial paper, non-U.S. government debt securities, supranational debt securities and U.S. Agency bonds. Available-for-sale securities are classified as either cash and cash equivalents or short-term investments on our unaudited condensed balance sheets.

The following tables summarize, by major security type, our short-term investments that are measured at fair value on a recurring basis, in thousands:


		June 30, 2022
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	1 or less	$	34,229	$	—	$	—		$	34,229

Short-term investments:
U.S. Treasury securities	2 or less		155,198		—		(2,733	)		152,465
Corporate debt securities	3 or less		145,296		—		(3,976	)		141,320
Commercial paper	1 or less		82,981		—		—			82,981
Non-U.S. government and supranational debt securities	2 or less		26,335		—		(870	)		25,465
U.S. Agency bonds	2 or less		8,996		—		(226	)		8,770
Total short-term investments			418,806		—		(7,805	)		411,001
Total		$	453,035	$	—	$	(7,805	)	$	445,230


		December 31, 2021
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	1 or less	$	79,895	$	—	$	—		$	79,895

Short-term investments:
U.S. Treasury securities	3 or less		135,452		—		(619	)		134,833
Corporate debt securities	3 or less		208,064		—		(892	)		207,172
Commercial paper	1 or less		53,439		—		—			53,439
Non-U.S. government and supranational debt securities	3 or less		23,122		—		(214	)		22,908
U.S. Agency bonds	2 or less		8,994		—		(58	)		8,936
Total short-term investments			429,071		—		(1,783	)		427,288
Total		$	508,966	$	—	$	(1,783	)	$	507,183

Short-term investments are classified as current assets, even though the stated maturity date may be one year or more beyond the current balance sheet date, which reflects management’s intention to use the proceeds from sales of these securities

to fund our operations, as necessary. As of June 30, 2022 and December 31, 2021, short-term investments of $251.8 million and $246.9 million, respectively, had maturities less than one year, and short-term investments of $159.2 million and $180.4 million, respectively, had maturities between one to three years. We had no realized gains or losses for the six months ended June 30, 2022 and 2021.

As of June 30, 2022, 34 available-for-sale securities with a fair market value of $328.0 million were in gross unrealized loss positions, $17.3 million of which were in a continuous unrealized loss position for greater than 12 months. We do not intend to sell these available-for-sale securities, and it is not more likely than not that we will be required to sell these securities prior to recovery of their amortized cost basis. Based on our review of these available-for-sale securities, the unrealized losses at June 30, 2022 were primarily due to changes in interest rates and not due to increased credit risks associated with specific securities. We have no allowance for credit losses as of June 30, 2022 and December 31, 2021. Unrealized gains and losses that are not credit-related are included in accumulated other comprehensive (income) loss.

Accrued interest receivable on available-for-sale securities were $1.2 million and $1.4 million at June 30, 2022 and December 31, 2021, respectively. We have not written off any accrued interest receivables for the six months ended June 30, 2022 and 2021.