U.S. GAAP establishes a three-tier fair value hierarchy to classify and disclose all assets and liabilities measured at fair value on a recurring basis, as well as assets and liabilities measured at fair value on a non-recurring basis, in periods subsequent to their initial measurement. The hierarchy requires us to use observable inputs when available and to minimize the use of unobservable inputs when determining fair value. The three tiers are defined as follows:

•Level 3. Unobservable inputs for which there is little or no market data, and which require us to develop our own estimates and assumptions reflecting those that a market participant would use.

The asset or liability’s fair value measurement level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Valuation techniques maximize the use of relevant observable inputs and minimize the use of unobservable inputs. There were no instruments measured at fair value on a recurring basis using significant unobservable inputs during the years ended December 31, 2022 and 2021.

•Market approach. Uses prices and other relevant information generated by market transactions involving identical or comparable assets or liabilities;

•Income approach. Uses valuation techniques to convert future amounts to a single present amount based on current market expectations about those future amounts; and

•Cost approach. Based on the amount that currently would be required to replace the service capacity of an asset (i.e., replacement cost).

The carrying amounts of our cash and cash equivalents, accounts receivable, accounts payable, and accrued expenses approximate fair value as of December 31, 2022 and 2021 because of the relatively short duration of these instruments. Additionally, the carrying value of our debt associated with the term loan facility approximates fair value because the interest rates are variable and reset on a relatively short durations to the then market rates.

Our investment portfolio consists largely of debt investments classified as available-for-sale. Changes in the fair value of available-for-sale securities, excluding other-than-temporary impairments, are recorded in accumulated other comprehensive loss in our consolidated balance sheets. The components of our investments as of December 31, 2022 and 2021 are as follows (in thousands):


	As of December 31, 2022
	Fair Value Measurement							Balance Sheet Classification
	Fair Value Level	Cost Basis		Unrealized Gains (Losses)		Market Value		Cash and Cash Equivalents		Short-term Investments and Marketable Securities
Money market fund	Level 1	$	39,469	$	—	$	39,469	$	39,469	$	—
U.S. Treasury bonds	Level 1	9,396		(13)		9,383		—		9,383
Commercial paper	Level 2	26,704		—		26,704		—		26,704
Corporate bonds	Level 2	9,353		(12)		9,341		—		9,341
Agency bonds	Level 2	2,432		3		2,435				2,435

Total investments		$	87,354	$	(22)	$	87,332	$	39,469	$	47,863


	As of December 31, 2021
	Fair Value Measurement							Balance Sheet Classification
	Fair Value Level	Cost Basis		Unrealized Gains (Losses)		Market Value		Cash and Cash Equivalents		Short-Term Investments and Marketable Securities		Long-Term Investments
Money market fund	Level 1	$	38,301	$	—	$	38,301	$	38,301	$	—	$	—
U.S. Treasury bonds	Level 1	8,171		—		8,171		—		8,171		—
Commercial paper	Level 2	23,312		—		23,312		—		23,312		—
Corporate bonds	Level 2	20,107		(14)		20,093		—		8,049		12,044
Asset-backed securities	Level 2	15,655		(8)		15,647		—		15,647		—
Total investments		$	105,546	$	(22)	$	105,524	$	38,301	$	55,179	$	12,044

There were no Level 3 assets held at any point during the year ended December 31, 2022 and 2021. Additionally, there were no transfers between Levels 1 and 2 during the years ended December 31, 2022 and 2021. Interest income on our investments totaled $0.9 million for the year ended December 31, 2022.

The amortized cost basis and fair value of debt securities at December 31, 2022 and 2021, by contractual maturity, are as follows (in thousands):


	As of December 31, 2022
	Cost Basis		Fair Value
Due in one year or less	$	87,354	$	87,332
Due after one year through five years	—		—
Total investments	$	87,354	$	87,332


	As of December 31, 2021
	Cost Basis		Fair Value
Due in one year or less	$	93,497	$	93,480
Due after one year through five years	12,049		12,044
Total investments	$	105,546	$	105,524

Actual maturities may differ from the contractual maturities in the table above because borrowers have the right to call or prepay certain obligations.