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 April 30, 2018, January 31, 2018 and April 30, 2017 were as follows:

	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		(Losses)			Value
As of April 30, 2018
Short-term Investments:
Corporate bonds	$	110,657	$	—	$	(294	)	$	110,363
Municipal and pre-refunded municipal bonds		54,659		—		(47	)		54,612
Certificates of deposit		1,392		—		—			1,392
		166,708		—		(341	)		166,367
Long-term Investments:
Corporate bonds		18,137		—		(212	)		17,925
Municipal and pre-refunded municipal bonds		7,873		—		(30	)		7,843
Mutual funds, held in rabbi trust		6,453		33		(3	)		6,483
Certificates of deposit		2,828		—		—			2,828
		35,291		33		(245	)		35,079
	$	201,999	$	33	$	(586	)	$	201,446
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 April 30, 2017
Short-term Investments:
Corporate bonds	$	77,313	$	4	$	(58	)	$	77,259
Municipal and pre-refunded municipal bonds		40,788		24		(3	)		40,809
Certificates of deposit		425		—		—			425
		118,526		28		(61	)		118,493
Long-term Investments:
Corporate bonds		27,586		3		(36	)		27,553
Municipal and pre-refunded municipal bonds		4,758		17		—			4,775
Mutual funds, held in rabbi trust		5,011		62		(1	)		5,072
Certificates of deposit		1,051		—		—			1,051
		38,406		82		(37	)		38,451
	$	156,932	$	110	$	(98	)	$	156,944

Proceeds from the sales and maturities of available-for-sale securities were $57,400 and $64,903 for the three months ended April 30, 2018 and 2017, respectively. The Company included in “Other income, net,” in the Condensed Consolidated Statements of Income, a net realized loss of $13 for the three months ended April 30, 2018, and a net realized gain of $14 for the three months ended April 30, 2017. Amortization of discounts and premiums, net, resulted in a reduction of “Other income, net” of $634 and $803 for the three months ended April 30, 2018 and 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.