Financial Instruments (Tables)

9 Months Ended

Oct. 31, 2018

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, 2018 and October 31, 2018 (in thousands):

	As of 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

	As of October 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Cash Equivalents		Marketable Securities		Restricted Cash
Level 1
Money market accounts	$	—	$	—	$	—		$	26,298	$	10,476	$	—	$	15,822
Level 2
U.S. government treasury notes	323,212		—		(891		)	322,321		62,392		259,929		—
U.S. government agencies	73,362		—		(355		)	73,007		2,992		70,015		—
Corporate debt securities	377,468		31		(1,830		)	375,669		—		375,669		—
Foreign government bonds	6,657		1		(14		)	6,644		—		6,644		—
Asset-backed securities	24,804		—		(41		)	24,763		—		24,763		—
Total	$	805,503	$	32	$	(3,131	)	$	828,702	$	75,860	$	737,020	$	15,822

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, 2018
	Amortized Cost		Fair Value
Due within one year	$	367,860	$	366,886
Due in one to five years	372,255		370,134
Total	$	740,115	$	737,020

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 position as of October 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	$	282,905	$	(535	)	$	39,416	$	(356	)	$	322,321	$	(891	)
U.S. government agencies	47,927		(143		)	25,080		(212		)	73,007		(355		)
Corporate debt securities	270,140		(1,080		)	72,743		(750		)	342,883		(1,830		)
Foreign government bonds	5,145		(14		)	—		—			5,145		(14		)
Asset-backed securities	24,763		(41		)	—		—			24,763		(41		)
Total	$	630,880	$	(1,813	)	$	137,239	$	(1,318	)	$	768,119	$	(3,131	)