Short-Term Investments (Tables)

9 Months Ended

Oct. 31, 2018

Investments Debt And Equity Securities [Abstract]

Schedule of Short-Term Investments

At October 31, 2018, short-term investments consisted of the following (in thousands):

			Gross		Gross			Estimated
	Amortized		unrealized		unrealized			fair
	cost		gains		losses			value
Available-for-sale securities:
Certificates of deposits	$	9,540	$	8	$	(1	)	$	9,547
Asset-backed securities		80,663		3		(502	)		80,164
Commercial paper		4,969		—		—			4,969
Corporate notes and bonds		172,815		30		(758	)		172,087
Foreign government bonds		3,001		—		(20	)		2,981
Mortgage backed securities		6,133		—		(14	)		6,119
U.S. agency obligations		35,744		—		(21	)		35,723
U.S. treasury securities		272,910		—		(217	)		272,693
Total available-for-sale securities	$	585,775	$	41	$	(1,533	)	$	584,283

At January 31, 2018, short-term investments consisted of the following (in thousands):  

			Gross		Gross			Estimated
	Amortized		unrealized		unrealized			fair
	cost		gains		losses			value
Available-for-sale securities:
Asset-backed securities	$	67,875	$	—	$	(424	)	$	67,451
Commercial paper		19,926		—		(12	)		19,914
Corporate notes and bonds		160,499		1		(759	)		159,741
Foreign government bonds		1,504		—		(18	)		1,486
Mortgage backed securities		11,555		—		(75	)		11,480
U.S. agency obligations		71,206		1		(76	)		71,131
U.S. treasury securities		110,707		5		(136	)		110,576
Total available-for-sale securities	$	443,272	$	7	$	(1,500	)	$	441,779

Summary of Estimated Fair Value of Short-Term Investments, Designated as Available-for-Sale and Classified by Contractual Maturity

The following table summarizes the estimated fair value of our short-term investments, designated as available-for-sale and classified by the contractual maturity date of the securities as of the dates shown (in thousands):

	October 31,	January 31,
	2018	2018
Due in one year or less	$409,337	$308,172
Due in greater than one year	174,946	133,607
Total	$584,283	$441,779

Schedule of Fair Values and Gross Unrealized Losses of Available-for-Sale Securities Aggregated by Investment Category

The following table shows the fair values and the gross unrealized losses of these available-for-sale securities aggregated by investment category as of October 31, 2018 (in thousands):  

			Gross
	Fair		unrealized
	value		losses
Certificates of deposits	$	999	$	(1	)
Asset-backed securities		77,636		(502	)
Commercial paper		4,968		—
Corporate notes and bonds		144,369		(758	)
Foreign government bonds		2,981		(20	)
Mortgage backed securities		5,638		(14	)
U.S. agency obligations		35,723		(21	)
U.S. treasury securities		248,754		(217	)

The following table shows the fair values and the gross unrealized losses of these available-for-sale securities aggregated by investment category as of January 31, 2018 (in thousands):

			Gross
	Fair		unrealized
	value		losses
Asset-backed securities	$	65,690	$	(424	)
Commercial paper		19,914		(12	)
Corporate notes and bonds		155,419		(759	)
Foreign government bonds		1,485		(18	)
Mortgage backed securities		11,481		(75	)
U.S. agency obligations		66,655		(76	)
U.S. treasury securities		82,147		(136	)