Short-term investments, principally U.S. Treasury bills, are available-for-sale and consisted of the following (in thousands):


	As of December 31, 2022
	Amortized Cost		Unrealized Loss, Net			Estimated Fair Value
U.S. Treasury securities	$	94,043	$	(75	)	$	93,968

	As of December 31, 2021
	Amortized Cost		Unrealized Loss, Net			Estimated Fair Value
U.S. Treasury securities	$	134,980	$	(9	)	$	134,971

All available-for-sale securities held as of December 31, 2022 and 2021 had a maturity of less than one year. The Company has classified all marketable securities, regardless of maturity, as short-term investments based upon the Company’s ability and intent to use any and all of those marketable securities to satisfy the Company’s liquidity requirements.

At each reporting date, the Company performs an evaluation of impairment to determine if any unrealized losses are the result of credit losses. Impairment is assessed at the individual security level. Factors considered in determining whether a loss resulted from a credit loss or other factors include the Company’s intent and ability to hold the investment until the recovery of its amortized cost basis, the extent to which the fair value is less than the amortized cost basis, the length of time and extent to which fair value has been less than the cost basis, the financial condition of the issuer, any historical failure of the issuer to make scheduled interest or principal payments, any changes to the rating of the security by a rating agency, any adverse legal or regulatory events affecting the issuer or issuer’s industry, and any significant deterioration in economic conditions.

The credit-related portion of unrealized losses, and any subsequent improvements, are recorded in interest expense in the consolidated statements of operations through an allowance for credit losses. Unrealized gains and losses that are not credit-related are included in accumulated other comprehensive loss. Unrealized losses on available-for-sale debt securities as of December 31, 2022 and December 31, 2021 were not significant and were primarily due to changes in interest rates, including market credit spreads, and not due to increased credit risks associated with specific securities. Further, the Company does not intend to sell these investments and it is not more likely than not that the Company will be required to sell these investments before recovery of their amortized cost basis. Accordingly, the Company did not record an allowance for credit losses with these investments as of December 31, 2022 and December 31, 2021.