Marketable Securities (Tables)

12 Months Ended

Jan. 31, 2019

Investments Debt And Equity Securities [Abstract]

Amortized Cost, Gross Unrealized Gains (Losses) and Fair Value of Available-For-Sale Securities

The amortized cost, gross unrealized gains (losses) and fair values of available-for-sale securities by major security type and class of security as of January 31, 2019 and 2018 are as follows:

	Amortized Cost		Unrealized Gains		Unrealized (Losses)			Fair Value
As of January 31, 2019
Short-term Investments:
Corporate bonds	$	227,287	$	24	$	(214	)	$	227,097
Municipal and pre-refunded municipal bonds		43,677		15		(18	)		43,674
Federal government agencies		1,458		—		—			1,458
Certificate of deposit		1,050		—		—			1,050
Commercial paper		2,979		—		—			2,979
Treasury bills		2,975		—		(1	)		2,974
		279,426		39		(233	)		279,232
Long-term Investments:
Corporate bonds		34,265		34		(63	)		34,236
Municipal and pre-refunded municipal bonds		7,554		7		(3	)		7,558
Federal government agencies		6,603		2		(1	)		6,604
Mutual funds, held in rabbi trust		6,301		450		—			6,751
Certificates of deposit		2,143		—		—			2,143
		56,866		493		(67	)		57,292
	$	336,292	$	532	$	(300	)	$	336,524

As of January 31, 2018
Short-term Investments:
Corporate bonds	$	111,612	$	—	$	(184	)	$	111,428
Municipal and pre-refunded municipal bonds		52,474		11		(39	)		52,446
Certificates of deposit		1,251		—		—			1,251
		165,337		11		(223	)		165,125
Long-term Investments:
Corporate bonds		39,853		—		(228	)		39,625
Municipal and pre-refunded municipal bonds		9,873		8		(24	)		9,857
Mutual funds, held in rabbi trust		5,973		274		(10	)		6,237
Certificates of deposit		2,969		—		—			2,969
		58,668		282		(262	)		58,688
	$	224,005	$	293	$	(485	)	$	223,813

Gross Unrealized Losses and Fair Value of Marketable Securities

The following tables show the gross unrealized losses and fair value of the Company’s marketable securities with unrealized losses that are not deemed to be other-than-temporarily impaired aggregated by the length of time that individual securities have been in a continuous unrealized loss position, at January 31, 2019 and 2018, respectively.

	January 31, 2019
	Less Than 12 Months					12 Months or Greater					Total
Description of Securities	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Corporate bonds	$	177,932	$	(160	)	$	38,201	$	(117	)	$	216,133	$	(277	)
Municipal and pre-refunded municipal bonds		20,732		(13	)		4,907		(8	)		25,639		(21	)
Federal government agencies		3,315		(1	)		—		—			3,315		(1	)
Treasury bills		2,974		(1	)		—		—			2,974		(1	)
Total	$	204,953	$	(175	)	$	43,108	$	(125	)	$	248,061	$	(300	)

	January 31, 2018
	Less Than 12 Months					12 Months or Greater				Total
Description of Securities	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Corporate bonds	$	151,053	$	(412	)	$	—	$	—	$	151,053	$	(412	)
Municipal and pre-refunded municipal bonds		39,671		(63	)		—		—		39,671		(63	)
Mutual funds, held in rabbi trust		474		(10	)		—		—		474		(10	)
Total	$	191,198	$	(485	)	$	—	$	—	$	191,198	$	(485	)