Financial Instruments (Tables)

12 Months Ended

Jan. 31, 2018

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, 2017 and 2018 (in thousands):



	January 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Cash Equivalents		Marketable Securities		Restricted Cash
Level 1
Money market accounts	$	—	$	—	$	—		$	12,734	$	—	$	—	$	12,734
Level 2
U.S. government treasury notes	148,298		22		(289		)	148,031		13,226		134,805		—
U.S. government agencies	40,398		2		(159		)	40,241		—		40,241		—
Corporate debt securities	185,701		242		(379		)	185,564		—		185,564		—
Foreign government bonds	2,377		2		(3		)	2,376		—		2,376		—
Total	$	376,774	$	268	$	(830	)	$	388,946	$	13,226	$	362,986	$	12,734



	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

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, 2018
	Amortized Cost		Fair Value
Due within one year	$	173,537	$	173,278
Due in one to five years	181,669		180,011
Total	$	355,206	$	353,289

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, 2018, 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	$	68,212	$	(219	)	$	52,607	$	(432	)	$	120,819	$	(651	)
U.S. government agencies	23,004		(156		)	23,892		(177		)	46,896		(333		)
Corporate debt securities	117,165		(732		)	33,132		(317		)	150,297		(1,049		)
Total	$	208,381	$	(1,107	)	$	109,631	$	(926	)	$	318,012	$	(2,033	)