The amortized cost, unrealized gains and losses and estimated fair value of the Company’s held-to-maturity marketable securities as of March 31, 2021 and December 31, 2020 were as follows:

	March 31, 2021
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents
Commercial paper	$	12,858	$	—	$	(3	)	$	12,855
Short-term investments
Commercial paper		50,203		—		(32	)		50,171
Corporate bonds		5,621		—		(1	)		5,620
Total	$	68,682	$	—	$	(36	)	$	68,646

	December 31, 2020
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents
Commercial paper	$	15,498	$	—	$	(3	)	$	15,495
Short-term investments
Commercial paper		46,978		—		(33	)		46,945
Corporate bonds		6,148		1		(1	)		6,148
Total	$	68,624	$	1	$	(37	)	$	68,588

All of the Company’s marketable securities were classified as held-to-maturity investments and have maturities within one year of March 31, 2021. The Company evaluated its marketable securities aggregated by credit rating agency rating, all of which are highly rated, investment grade securities, considering historical investment losses, current market conditions and historical recovery rates of similar securities and determined that no material credit losses were expected as of March 31, 2021.

The gross unrealized losses, estimated fair value and length of time the individual marketable securities were in a continuous loss position for those marketable securities in an unrealized loss position as of March 31, 2021 and December 31, 2020 were as follows:

	March 31, 2021
	Less Than 12 Months					12 Months or Greater				Total
	Estimated Fair Value		Unrealized Loss			Estimated Fair Value		Unrealized Loss		Estimated Fair Value		Unrealized Loss
	(in thousands)
Commercial paper	$	63,026	$	(35	)	$	—	$	—	$	63,026	$	(35	)
Corporate bonds		4,119		(1	)		—		—		4,119		(1	)
Total	$	67,145	$	(36	)	$	—	$	—	$	67,145	$	(36	)

	December 31, 2020
	Less Than 12 Months					12 Months or Greater				Total
	Estimated Fair Value		Unrealized Loss			Estimated Fair Value		Unrealized Loss		Estimated Fair Value		Unrealized Loss
	(in thousands)
Commercial paper	$	62,440	$	(36	)	$	—	$	—	$	62,440	$	(36	)
Corporate bonds		4,569		(1	)		—		—		4,569		(1	)
Total	$	67,009	$	(37	)	$	—	$	—	$	67,009	$	(37	)

The Company recognized interest income during the three months ended March 31, 2021 and 2020 of $0.1 million and $0.9 million, respectively, within net interest expense on the condensed consolidated statements of operations. During the three months ended March 31, 2021 and 2020, the Company did not recognize any other-than-temporary impairment losses related to its marketable securities.

The Company’s marketable securities are classified within Level 2 of the fair value hierarchy (see Note 13, Fair Value Measurement, for further details).