4. Marketable Securities

During all periods shown, marketable securities are classified as available-for-sale. 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

Proceeds from the sales and maturities of available-for-sale securities were $130,029 and $152,838 for the six months ended July 31, 2018 and 2017, respectively. The Company included in “Other income, net,” in the Condensed Consolidated Statements of Income, net realized losses of $0 and $13 for the three and six months ended July 31, 2018, respectively, and net realized losses of $23 and $9 for the three and six months ended July 31, 2017, respectively. Amortization of discounts and premiums, net, resulted in a reduction of “Other income, net” of $517 and $1,151 for the three and six months ended July 31, 2018, respectively, and $725 and $1,528 for the three and six months ended July 31, 2017, respectively. Mutual funds represent assets held in an irrevocable rabbi trust for the Company’s Non-qualified Deferred Compensation Plan (“NQDC”). These assets are a source of funds to match the funding obligations to participants in the NQDC but are subject to the Company’s general creditors. The Company elected the fair value option for financial assets for the mutual funds held in the rabbi trust resulting in all unrealized gains and losses being recorded in “Other income, net” in the Condensed Consolidated Statements of Income.