Financial Instruments (Tables)

9 Months Ended

Oct. 31, 2017

Investments, Debt and Equity Securities [Abstract]

Summary of Cash Equivalents, Marketable Securities and Restricted Cash by Significant Investment Categories

The following tables summarize our cash equivalents, marketable securities and restricted cash by significant investment categories as of January 31, 2017 and October 31, 2017 (in thousands):

	As of 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

	As of October 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Cash Equivalents		Marketable Securities		Restricted Cash
Level 1
Money market accounts	$	—	$	—	$	—		$	14,763	$	—	$	—	$	14,763
Level 2
U.S. government treasury notes	144,297		6		(419		)	143,884		6,374		137,510		—
U.S. government agencies	44,517		—		(205		)	44,312		—		44,312		—
Corporate debt securities	187,616		209		(310		)	187,515		—		187,515		—
Total	$	376,430	$	215	$	(934	)	$	390,474	$	6,374	$	369,337	$	14,763

Schedule of Amortized Cost and Estimated Fair Value of Marketable Securities by Contractual Maturity

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

	As of October 31, 2017
	Amortized Cost		Fair Value
Due within one year	$	173,537	$	173,413
Due in one to five years	196,519		195,924
Total	$	370,056	$	369,337

Schedule of Gross Unrealized Losses and Fair Values for Investments that were in Continuous Unrealized Loss Position for Less Than 12 Months, Aggregated by Investments Category

The following table presents gross unrealized losses and fair values for those investments that were in a continuous unrealized loss as of October 31, 2017, 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	$	122,530	$	(381	)	$	3,965	$	(38	)	$	126,495	$	(419	)
U.S. government agencies	31,914		(106		)	12,398		(99		)	44,312		(205		)
Corporate debt securities	81,288		(168		)	24,941		(142		)	106,229		(310		)
Total	$	235,732	$	(655	)	$	41,304	$	(279	)	$	277,036	$	(934	)