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 June 30, 2022:	Input Level	Cost			Gain		Loss			Fair Value
		(in thousands)
Money market funds	Level 1	$	43,419		$	—	$	—		$	43,419
U.S. Treasury obligations	Level 2		116,399			—		(722	)		115,677
Government agency obligations	Level 2		22,448			—		(167	)		22,281
Corporate debt obligations	Level 2		115,132			2		(1,627	)		113,507
Commercial paper	Level 2		23,453			—		—			23,453
Asset-backed securities	Level 2		11,800			—		(104	)		11,696
Total available-for-sale securities			332,651			2		(2,620	)		330,033
Less: amounts classified as cash equivalents			(69,411	)		—		1			(69,410	)
Amounts classified as short-term investments		$	263,240		$	2	$	(2,619	)	$	260,623

		Total			Total		Total			Total
		Amortized			Unrealized		Unrealized			Estimated
As of December 31, 2021:	Input Level	Cost			Gain		Loss			Fair Value
		(in thousands)
Money market funds	Level 1	$	89,738		$	—	$	—		$	89,738
U.S. Treasury obligations	Level 2		111,832			1		(138	)		111,695
Government agency obligations	Level 2		21,346			—		(23	)		21,323
Corporate debt obligations	Level 2		99,757			6		(190	)		99,573
Commercial paper	Level 2		36,993			—		—			36,993
Asset-backed securities	Level 2		10,174			1		(25	)		10,150
Total available-for-sale securities			369,840			8		(376	)		369,472
Less: amounts classified as cash equivalents			(104,488	)		—		—			(104,488	)
Amounts classified as short-term investments		$	265,352		$	8	$	(376	)	$	264,984

We considered the current and expected future global economic and market conditions, including the COVID-19 pandemic and the war in Ukraine, and determined that our investments have not been significantly impacted. As of June 30, 2022, 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 the Company has 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 six months ended June 30, 2022 and 2021, 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 prepaid expenses and other current assets, separate from short-term investments on our condensed consolidated balance sheet. As of June 30, 2022 and December 31, 2021, accrued interest receivable was $0.9 million and $0.8 million, respectively. We have not written off any accrued interest receivables during the six months ended June 30, 2022 and 2021.

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. As of June 30, 2022 and December 31, 2021, restricted cash was $1.3 million and $1.4 million, respectively.