	June 30, 2021
	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Corporate bonds	$	466,403	$	111	$	(55	)	$	466,459
U.S. treasury securities		155,663		16		(5	)		155,674
Asset-backed securities		26,391		16		(1	)		26,406
Certificates of deposit		6,775		—		—			6,775
	$	655,232	$	143	$	(61	)	$	655,314

	June 30, 2020
	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Corporate bonds	$	70,781	$	360	$	(10	)	$	71,131
U.S. treasury securities		28,281		88		(1	)		28,368
Asset-backed securities		24,333		142		—			24,475
	$	123,395	$	590	$	(11	)	$	123,974

The amortized cost and fair value amounts include accrued interest receivable of $2.5 million and $0.5 million at June 30, 2021 and 2020, respectively. See Note 4 for additional information about the fair value measurement of short-term investments.

As of June 30, 2021, the fair value of the Company’s short-term investments that mature within one year and thereafter was $495.8 million and $159.5 million, respectively, or 76% and 24%, respectively, of the Company’s total short-term investments. As of June 30, 2020, the fair value of the Company’s short-term investments that mature within one year and thereafter was $102.9 million and $21.1 million, respectively, or 83% and 17%, respectively, of the Company’s total short-term investments.

As of June 30, 2021, approximately 100 of the more than 300 investment positions were in an unrealized loss position. The following table presents the gross unrealized losses and fair values of those investments that were in an unrealized loss position as of the dates presented (in thousands):

	June 30, 2021
	Fair value		Unrealized losses
Corporate bonds	$	152,485	$	(55	)
U.S. treasury securities		85,466		(5	)
Asset backed securities		8,089		(1	)
Total	$	246,040	$	(61	)

	June 30, 2020
	Fair value		Unrealized losses
Corporate bonds	$	9,258	$	(10	)
U.S. treasury securities		2,798		(1	)
Total	$	12,056	$	(11	)

Most of the Company investments with unrealized losses had been in a continuous unrealized loss position for less than 12 months. Investments with unrealized losses that had been in a continuous unrealized loss position for more than 12 months have been insignificant. The Company does not intend to sell the investments and it is not likely that the Company will be required to sell the investments before recovery of their amortized cost bases, which may be at maturity. Therefore, the Company does not consider those unrealized investment losses as other-than-temporary impairment of the investments. There have been no significant realized gains or losses on the short-term investments during the years ended June 30, 2021, 2020 and 2019.

The Company has not recorded an allowance for credit losses on investments that were in an unrealized loss position as of June 30, 2021 because they were not significant.