Short-Term Investments (Tables)

6 Months Ended

Jul. 31, 2018

Investments Debt And Equity Securities [Abstract]

Schedule of Short-Term Investments

At July 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	$	11,036	$	7	$	—		$	11,043
Asset-backed securities		86,498		2		(555	)		85,945
Commercial paper		13,596		2		(1	)		13,597
Corporate notes and bonds		152,185		56		(718	)		151,523
Foreign government bonds		2,999		—		(21	)		2,978
Mortgage backed securities		13,366		—		(81	)		13,285
U.S. agency obligations		57,657		2		(25	)		57,634
U.S. treasury securities		162,888		1		(204	)		162,685
Total available-for-sale securities	$	500,225	$	70	$	(1,605	)	$	498,690

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):

	July 31,		January 31,
	2018		2018
Due in one year or less	$	331,500	$	308,172
Due in greater than one year		167,190		133,607
Total	$	498,690	$	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 July 31, 2018 (in thousands):  

			Gross
	Fair		unrealized
	value		losses
Asset-backed securities	$	82,019	$	(555	)
Commercial paper		3,892		(1	)
Corporate notes and bonds		108,287		(718	)
Foreign government bonds		2,979		(21	)
Mortgage backed securities		13,285		(81	)
U.S. agency obligations		49,893		(25	)
U.S. treasury securities		153,505		(204	)

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	)