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


	September 30, 2021
	Amortized Cost		Unrealized Gain		Unrealized Loss			Estimated Fair Value
Short-term marketable securities:
U.S. government debt securities	$	—	$	—	$	—		$	—
Corporate bonds		83,208		—		(9	)		83,199
Total short-term marketable securities	$	83,208	$	—	$	(9	)	$	83,199
Long-term marketable securities:
U.S. government debt securities	$	3,995	$	—	$	—		$	3,995
Corporate bonds		19,633		—		(9	)		19,624
Total long-term marketable securities	$	23,628	$	—	$	(9	)	$	23,619

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 $0.3 million is presented separately within the prepaid expenses and other current assets line items in the Company's unaudited condensed consolidated balance sheet as of September 30, 2021.

As of September 30, 2021, there were $45.9 million of corporate bonds 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.

As of September 30, 2021, 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 September 30, 2021 were considered to be impaired, as such, no impairment loss was recorded for the three and nine months ended September 30, 2021.