Financial Instruments (Tables)

12 Months Ended

Jan. 31, 2019

Fair Value, Assets Measured on Recurring Basis

The following tables summarize our cash equivalents, marketable securities and restricted cash by significant investment categories as of January 31, 2018 and 2019 (in thousands):



	January 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Cash Equivalents		Marketable Securities		Restricted Cash
Level 1
Money market accounts	$	—	$	—	$	—		$	32,057	$	17,294	$	—	$	14,763
Level 2
U.S. government treasury notes	131,643		—		(651		)	130,992		10,172		120,820		—
U.S. government agencies	47,229		—		(333		)	46,896		—		46,896		—
Corporate debt securities	186,506		116		(1,049		)	185,573		—		185,573		—
Total	$	365,378	$	116	$	(2,033	)	$	395,518	$	27,466	$	353,289	$	14,763



	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

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):



	January 31, 2019
	Amortized Cost		Fair Value
Due within one year	$	342,739	$	342,256
Due in one to five years	407,081		407,226
Total	$	749,820	$	749,482

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 as of January 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	$	156,529	$	(98	)	$	40,413	$	(217	)	$	196,942	$	(315	)
U.S. government agencies	24,892		(20		)	23,600		(134		)	48,492		(154		)
Corporate debt securities	83,577		(152		)	96,914		(605		)	180,491		(757		)
Asset-backed securities	11,194		(12		)	—		—			11,194		(12		)
Total	$	276,192	$	(282	)	$	160,927	$	(956	)	$	437,119	$	(1,238	)