Investment securities classified as available-for-sale consisted of the following at December 31, 2022 and 2021 (in thousands):


	December 31, 2022
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Corporate bonds	$	17,497	$	2	$	(112)	$	17,387
Agency securities	17,507		—		(484)		17,023

Treasury securities	81,605		—		(1,557)		80,048
Total available-for-sale investment securities	$	116,609	$	2	$	(2,153)	$	114,458


	December 31, 2021
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Corporate bonds	$	29,080	$	—	$	(11)	$	29,069
Agency securities	19,753		—		(27)		19,726
Treasury securities	77,108		2		(229)		76,881
Total available-for-sale investment securities	$	125,941	$	2	$	(267)	$	125,676

As of December 31, 2022, the decline in fair value below amortized cost basis was not considered other than temporary as it is more likely than not we will hold the securities until maturity or recovery of the cost basis. No allowance for credit losses for available-for-sale investment securities was recorded as of December 31, 2022 or 2021.

The fair values of available-for-sale investment securities, by remaining contractual maturity, are as follows (in thousands):


	December 31, 2022				December 31, 2021
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Due in one year or less	$	90,822	$	89,297	$	64,627	$	64,600
Due after one year through three years	25,787		25,161		61,314		61,076
Total available-for-sale investment securities	$	116,609	$	114,458	$	125,941	$	125,676

During the years ended December 31, 2022 and 2021, we had sales and maturities (which include calls) of investment securities, as follows (in thousands):


	Year Ended December 31, 2022
	Gross Realized Gains		Gross Realized Losses		Gross Proceeds from Sales		Gross Proceeds from Maturities
Corporate bonds	$	—	$	(3)	$	994	$	28,998
Agency securities	—		—		—		2,250

Treasury securities	—		—		—		56,635
	$	—	$	(3)	$	994	$	87,883


	Year Ended December 31, 2021
	Gross Realized Gains		Gross Realized Losses		Gross Proceeds from Sales		Gross Proceeds from Maturities
Corporate bonds	$	—	$	—	$	—	$	39,075
Agency securities	—		—		—		11,575

Treasury securities	6		—		43,198		56,704

	$	6	$	—	$	43,198	$	107,354

In December 2021, we sold all of our interest in SecureDocs. A gain of $12.8 million was recognized within Other income, net in our Consolidated Statements of Operations, a portion of which relates to the recovery of a $2.0 million note receivable which had been previously reserved.

The following tables present our financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2022 and 2021 by level within the fair value hierarchy (in thousands):


	December 31, 2022
	Level 1		Level 2		Total Fair Value
Cash equivalents:
Money market funds	$	41,973	$	—	$	41,973
Treasury securities	1,287		—		1,287
Available-for-sale investment securities:
Corporate bonds	—		17,387		17,387
Agency securities	—		17,023		17,023

Treasury securities	80,048		—		80,048
Total	$	123,308	$	34,410	$	157,718


	December 31, 2021
	Level 1		Level 2		Total Fair Value
Cash equivalents:
Money market funds	$	6,105	$	—	$	6,105

Available-for-sale investment securities:
Corporate bonds	—		29,069		29,069
Agency securities	—		19,726		19,726

Treasury securities	76,881		—		76,881
Total	$	82,986	$	48,795	$	131,781

The carrying amounts of cash and cash equivalents, restricted cash, accounts receivable, accounts payable and accrued liabilities approximate their fair value because of the short maturity of these items.

There were no changes to our valuation techniques used to measure asset and liability fair values on a recurring basis during the year ended December 31, 2022. The valuation techniques for the financial assets in the tables above are as follows:

At December 31, 2022 and 2021, cash equivalents include cash invested in money market funds and treasury securities with a maturity of three months or less. Fair value is based on market prices for identical assets.

Fair value for our Level 1 investment securities is based on market prices for identical assets. Our Level 2 securities were priced by a pricing vendor. The pricing vendor utilizes the most recent observable market information in pricing these securities or, if specific prices are not available for these securities, other observable inputs like market transactions involving comparable securities are used.