Financial Instruments (Tables)

12 Months Ended

Jan. 31, 2021

Fair Value Disclosures [Abstract]

Fair Value, Assets Measured on Recurring Basis

The following tables summarize our cash equivalents, marketable securities and restricted cash by significant investment categories and their classification within the fair value hierarchy at the end of fiscal 2020 and 2021 (in thousands):

	At the End of Fiscal 2020
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value		Cash Equivalents		Marketable Securities		Restricted Cash
Level 1
Money market accounts	$	—	$	—	$	—	$	26,355	$	11,068	$	—	$	15,287
Level 2
U.S. government treasury notes	323,751		2,146		—		325,897		—		325,897		—
U.S. government agencies	53,930		317		(3)		54,244		—		54,244		—
Corporate debt securities	452,318		3,954		(1)		456,271		3,001		453,270		—
Foreign government bonds	14,994		147		—		15,141		—		15,141		—
Asset-backed securities	87,267		699		—		87,966		—		87,966		—
Total	$	932,260	$	7,263	$	(4)	$	965,874	$	14,069	$	936,518	$	15,287

	At the End of Fiscal 2021
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value		Cash Equivalents		Marketable Securities		Restricted Cash
Level 1
Money market accounts	$	—	$	—	$	—	$	49,984	$	39,440	$	—	$	10,544
Level 2
U.S. government treasury notes	339,253		3,241		(1)		342,493		15,340		327,153		—
U.S. government agencies	56,729		516		—		57,245		—		57,245		—
Corporate debt securities	425,115		4,176		(33)		429,258		—		429,258		—
Foreign government bonds	21,486		307		—		21,793		—		21,793		—
Asset-backed securities	79,924		1,015		—		80,939		—		80,939		—
Total	$	922,507	$	9,255	$	(34)	$	981,712	$	54,780	$	916,388	$	10,544

Investments Classified by Contractual Maturity Date

The amortized cost and estimated fair value of our marketable securities are shown below by contractual maturity (in thousands):

	At the End of Fiscal 2021
	Amortized Cost		Fair Value
Due within one year	$	316,339	$	318,019
Due in one to five years	590,828		598,369
Total	$	907,167	$	916,388

Schedule of Unrealized Loss on Investments

The following table presents gross unrealized losses and fair values for those investments that were in a continuous unrealized loss position at the end of fiscal 2020 and 2021, aggregated by investment category (in thousands):

	At the End of Fiscal 2020
	Less than 12 months				Greater than 12 months				Total
	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
U.S. government treasury notes	$	—	$	—	$	1,000	$	—	$	1,000	$	—
U.S. government agencies	4,998		(3)		—		—		4,998		(3)
Corporate debt securities	9,691		(1)		—		—		9,691		(1)
Total	$	14,689	$	(4)	$	1,000	$	—	$	15,689	$	(4)

	At the End of Fiscal 2021
	Less than 12 months				Greater than 12 months				Total
	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
U.S. government treasury notes	$	8,301	$	(1)	$	—	$	—	$	8,301	$	(1)
Corporate debt securities	32,996		(33)		—		—		32,996		(33)
Total	$	41,297	$	(34)	$	—	$	—	$	41,297	$	(34)