The amortized cost, gross unrealized gains (losses) and fair value of available-for-sale securities by major security type and class of security as of July 31, 2018, January 31, 2018 and July 31, 2017 were as follows:

	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		(Losses)			Value
As of July 31, 2018
Short-term Investments:
Corporate bonds	$	150,648	$	—	$	(261	)	$	150,387
Municipal and pre-refunded municipal bonds		46,904		10		(43	)		46,871
Certificates of deposit		908		—		—			908
		198,460		10		(304	)		198,166
Long-term Investments:
Corporate bonds		34,333		—		(213	)		34,120
Municipal and pre-refunded municipal bonds		2,130		1		(7	)		2,124
Mutual funds, held in rabbi trust		6,401		171		(1	)		6,571
Certificates of deposit		2,699		—		—			2,699
		45,563		172		(221	)		45,514
	$	244,023	$	182	$	(525	)	$	243,680
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
As of July 31, 2017
Short-term Investments:
Corporate bonds	$	72,805	$	4	$	(61	)	$	72,748
Municipal and pre-refunded municipal bonds		36,630		15		(13	)		36,632
Certificates of deposit		815		—		—			815
		110,250		19		(74	)		110,195
Long-term Investments:
Corporate bonds		14,906		—		(22	)		14,884
Municipal and pre-refunded municipal bonds		3,057		9		(2	)		3,064
Mutual funds, held in rabbi trust		5,183		103		—			5,286
Certificates of deposit		2,726		—		—			2,726
		25,872		112		(24	)		25,960
	$	136,122	$	131	$	(98	)	$	136,155