Investments consists of available-for-sale securities as follows (in thousands):


	December 31, 2021
	Amortized Cost		Unrealized Gain		Unrealized Loss			Estimated Fair Value
Short-term marketable securities:
Commercial paper	$	54,363	$	—	$	(1	)	$	54,362
Corporate bonds		35,231		—		(35	)		35,196
Total short-term marketable securities		89,594		—		(36	)		89,558
Long-term marketable securities:
U.S. government debt securities		3,996		—		(17	)		3,979
Corporate bonds		21,010		—		(70	)		20,940
Total long-term marketable securities	$	25,006	$	—	$	(87	)	$	24,919

All the commercial paper, U.S. government debt securities, and corporate bonds designated as short-term marketable securities have a contractual maturity date that is equal to or less than one year from the respective balance sheet date. Those that are designated as long-term marketable securities have a contractual maturity date that is more than one year from the respective balance sheet date.

Accrued interest receivable is excluded from the amortized cost and estimated fair value of the Company's marketable securities. Accrued interest receivable of $0.5 million is presented separately within the prepaid expenses and other current assets line items in the Company's consolidated balance sheet as of December 31, 2021.

As of December 31, 2021, there were $60.1 million of corporate bonds and $4.0 million of commercial paper in a continual unrealized loss position for less than 12 months. There were no investments in a continual unrealized loss position for greater than twelve months.

Furthermore, the Company did not intend, nor was the Company more likely than not to be required, to sell its available-for-sale investments before the recovery of the amortized cost basis, which may be maturity. Based on the Company's assessment, it concluded that none of the available-for-sale investments held as of December 31, 2021 were considered to be other-than-temporarily impaired, as such, no impairment loss was recorded for the year ended December 31, 2021. There was no realized gain or loss on available-for-sale securities in the periods presented.