Financial Instruments - (Tables)

6 Months Ended

Jul. 31, 2019

Investments, Debt and Equity Securities [Abstract]

Cash Equivalents, Marketable Securities and Restricted Cash

The following tables summarize our cash equivalents, marketable securities and restricted cash by significant investment categories as of January 31, 2019 and July 31, 2019 (in thousands):

	As of January 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Cash Equivalents		Marketable Securities		Restricted Cash
Level 1
Money market accounts	$	—	$	—	$	—		$	43,038	$	27,215	$	—	$	15,823
Level 2
U.S. government treasury notes	315,329		208		(315		)	315,222		34,129		281,093		—
U.S. government agencies	69,114		17		(154		)	68,977		9,983		58,994		—
Corporate debt securities	363,860		534		(757		)	363,637		—		363,637		—
Foreign government bonds	7,965		36		—			8,001		—		8,001		—
Asset-backed securities	37,664		105		(12		)	37,757		—		37,757		—
Total	$	793,932	$	900	$	(1,238	)	$	836,632	$	71,327	$	749,482	$	15,823

	As of July 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Cash Equivalents		Marketable Securities		Restricted Cash
Level 1
Money market accounts	$	—	$	—	$	—		$	36,659	$	21,234	$	—	$	15,425
Level 2
U.S. government treasury notes	348,463		1,454		(58		)	349,859		—		349,859		—
U.S. government agencies	66,153		222		(22		)	66,353		—		66,353		—
Corporate debt securities	427,362		2,685		(111		)	429,936		1,029		428,907		—
Foreign government bonds	8,480		100		—			8,580		—		8,580		—
Asset-backed securities	59,504		329		(11		)	59,822		—		59,822		—
Total	$	909,962	$	4,790	$	(202	)	$	951,209	$	22,263	$	913,521	$	15,425

Amortized Cost and Estimated Fair Value

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

	As of July 31, 2019
	Amortized Cost		Fair Value
Due within one year	$	336,156	$	336,736
Due in one to five years	572,777		576,785
Total	$	908,933	$	913,521

Gross Unrealized Losses and Fair Values

The following table presents gross unrealized losses and fair values for those investments that were in a continuous unrealized loss position as of July 31, 2019, aggregated by investment category (in thousands):

	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	$	27,887	$	(30	)	$	9,737	$	(28	)	$	37,624	$	(58	)
U.S. government agencies	5,215		(7		)	9,183		(15		)	14,398		(22		)
Corporate debt securities	38,856		(28		)	43,245		(83		)	82,101		(111		)
Asset-backed securities	9,399		(11		)	—		—			9,399		(11		)
Total	$	81,357	$	(76	)	$	62,165	$	(126	)	$	143,522	$	(202	)