Our financial assets are measured at fair value on a recurring basis using the following hierarchy to prioritize valuation inputs, in accordance with applicable U.S. GAAP:

Level 1: Quoted prices in active markets for identical assets or liabilities that we have the ability to access

Level 2: Observable market-based inputs or unobservable inputs that are corroborated by market data such as quoted prices, interest rates and yield curves

Level 3: Inputs that are unobservable data points that are not corroborated by market data

We review the fair value hierarchy classification on a quarterly basis. Changes in the ability to observe valuation inputs may result in a reclassification of levels of certain securities within the fair value hierarchy. We recognize transfers into and out of levels within the fair value hierarchy in the period in which the actual event or change in circumstances that caused the transfer occurs. There have been no transfers between Level 1, Level 2 and Level 3 in any periods presented.

Financial assets and liabilities are considered Level 2 when their fair values are determined using inputs that are observable in the market or can be derived principally from or corroborated by observable market data such as pricing for similar securities, recently executed transactions, cash flow models with yield curves, and benchmark securities. In addition, Level 2 financial instruments are valued using comparisons to like-kind financial instruments and models that use readily observable market data as their basis. U.S. Treasury, government agency and corporate debt obligations, commercial paper and asset-backed securities are valued primarily using market prices of comparable securities, bid/ask quotes, interest rate yields and prepayment spreads and are included in Level 2.

Financial assets and liabilities are considered Level 3 when their fair values are determined using pricing models, discounted cash flow methodologies, or similar techniques, and at least one significant model assumption or input is unobservable. We have no Level 3 financial assets or liabilities.

The following tables summarize the estimated fair value and related valuation input hierarchy of our available-for-sale securities as of each period end:


		Total			Total			Total			Total
		Amortized			Unrealized			Unrealized			Estimated
As of September 30, 2023:	Input Level	Cost			Gain			Loss			Fair Value
		(in thousands)
Money market funds	Level 1	$	35,230		$	—		$	—		$	35,230
U.S. Treasury obligations	Level 2		28,318			4			—		$	28,322
Government agency obligations	Level 2		1,451			—			(26	)	$	1,425
Corporate debt obligations	Level 2		34,018			—			(509	)	$	33,509
Asset-backed securities	Level 2		2,723			—			(40	)	$	2,683
Total available-for-sale securities			101,740			4			(575	)		101,169
Less: amounts classified as cash equivalents			(63,548	)		(4	)		—			(63,552	)
Amounts classified as short-term investments		$	38,192		$	—		$	(575	)	$	37,617

		Total			Total			Total			Total
		Amortized			Unrealized			Unrealized			Estimated
As of December 31, 2022:	Input Level	Cost			Gain			Loss			Fair Value
		(in thousands)
Money market funds	Level 1	$	78,033		$	—		$	—		$	78,033
U.S. Treasury obligations	Level 2		63,013			3			(394	)		62,622
Government agency obligations	Level 2		8,086			—			(48	)		8,038
Corporate debt obligations	Level 2		82,598			4			(1,513	)		81,089
Commercial paper	Level 2		996			—			—			996
Asset-backed securities	Level 2		6,343			—			(119	)		6,224
Total available-for-sale securities			239,069			7			(2,074	)		237,002
Less: amounts classified as cash equivalents			(87,122	)		(3	)		—			(87,125	)
Amounts classified as short-term investments		$	151,947		$	4		$	(2,074	)	$	149,877

The amortized cost and fair value of our available-for-sale securities by contractual maturity were as follows:


	As of September 30, 2023				As of December 31, 2022
	Amortized		Estimated		Amortized		Estimated
	Cost		Fair Value		Cost		Fair Value
	(in thousands)				(in thousands)
Maturing within one year	$	97,367	$	96,863	$	202,323	$	201,359
Maturing in one to five years		4,373		4,306		36,746		35,643
Total available-for-sale securities	$	101,740	$	101,169	$	239,069	$	237,002

We considered the current and expected future global economic and market conditions, including, but not limited to, the wars in Ukraine and the Middle East and increased tensions between the U.S. and China, and determined that our investments have not been significantly impacted. As of September 30, 2023, no significant facts or circumstances were present to indicate a deterioration in the creditworthiness of the issuers of the available-for-sale securities we hold, and we have no requirement or intention to sell these securities before maturity or recovery of their amortized cost basis. For all securities with a fair value less than its amortized cost basis, we determined the decline in fair value below amortized cost basis to be non-credit related and no allowance for losses has been recorded. During the three and nine months ended September 30, 2023 and 2022, we did not recognize any impairment losses on our investments.

We have elected the practical expedient to exclude the applicable accrued interest from both the fair value and the amortized cost basis of our available-for-sale securities for purposes of identifying and measuring an impairment. We present accrued interest receivable related to our available-for-sale securities in other current assets, separate from short-term investments, on our condensed consolidated balance sheet. As of September 30, 2023 and December 31, 2022, accrued interest receivable was $0.4 million and $0.8 million, respectively. We have not written off any accrued interest receivables during the three and nine months ended September 30, 2023 and 2022.

In addition, restricted cash collateralized by money market funds is a financial asset measured at fair value and is a Level 1 financial instrument under the fair value hierarchy.