4. INVESTMENT SECURITIES, AVAILABLE-FOR-SALE AND FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2022

Investments, All Other Investments [Abstract]

Schedule of Fair Value Hierarchy Assets and Liabilities

The valuation inputs hierarchy classification for assets measured at fair value on a recurring basis are summarized below as of December 31, 2022 and 2021 (in thousands). These tables do not include cash held in our money market savings accounts.

As of December 31, 2022	Level 1		Level 2		Level 3		Total
Assets
Corporate debt securities	$	—	$	15,500	$	—	$	15,500
U.S. Treasury securities		—		46,673		—		46,673
	$	—	$	62,173	$	—	$	62,173
As of December 31, 2021	Level 1		Level 2		Level 3		Total
Assets
Corporate debt securities	$	—	$	32,720	$	—	$	32,720
	$	—	$	32,720	$	—	$	32,720

Schedule of Unrealized Gain or Loss on Short-term Investments

Our short-term investments are summarized below as of December 31, 2022 and 2021 (in thousands).

								Investment
	Cost/		Gross		Gross			Securities,
	Amortized		Unrealized		Unrealized			Available-
	Cost		Gains		Losses			For-Sale
As of December 31, 2022
Assets
Corporate debt securities	$	15,538	$	—	$	(38	)	$	15,500
U.S. Treasury securities		46,762		2		(91	)		46,673
	$	62,300	$	2	$	(129	)	$	62,173
As of December 31, 2021
Assets
Corporate debt securities	$	32,739	$	3	$	(22	)	$	32,720
	$	32,739	$	3	$	(22	)	$	32,720

+Maturity Date of Available-for-sale Securities

The maturities of the investment securities available-for-sale as of December 31, 2022 and 2021 are shown below (in thousands):

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
As of December 31, 2022
Maturity date
Less than one year	$	62,300	$	2	$	(129	)	$	62,173
	$	62,300						$	62,173
As of December 31, 2021
Less than one year	$	32,739	$	3	$	(22	)	$	32,720
	$	32,739						$	32,720

Schedule of Unrealized Loss on Investment Securities

The following table summarizes investments that have been in a continuous unrealized loss position for less than 12 months and those that have been in a continuous unrealized loss position for more than 12 months as of December 31, 2022 and 2021 (in thousands):

	Less than Twelve Months					Twelve Months or Greater				Total
			Gross					Gross				Gross
	Fair		Unrealized			Fair		Unrealized		Fair		Unrealized
	Value		Losses			Value		Losses		Value		Losses
As of December 31, 2022
Corporate debt securities	$	12,295	$	(38	)	$	—	$	—		12,295		(38	)
U.S. Treasury securities		34,530		(91	)		—		—		34,530		(91	)
	$	46,825	$	(129	)	$	—	$	—	$	46,825	$	(129	)
As of December 31, 2021
Corporate debt securities	$	27,195	$	(22	)	$	—	$	—		27,195		(22	)
	$	27,195	$	(22	)	$	—	$	—	$	27,195	$	(22	)