3. Investments

Investments consist of the following (in thousands):


	July 28,		April 30,
	2018		2018
Short-term investments:
Held-to-maturity securities:
Municipal securities	$	14,964	$	35,344
U.S. government securities		33,514		31,620
Corporate bonds		66,825		46,685
Certificates of deposit		3,000		—
Total held-to-maturity and short-term investments	$	118,303	$	113,649
Long-term investments:
Held-to-maturity securities:
Municipal securities	$	2,031	$	2,046
U.S. government securities		28,809		27,356
Corporate bonds		5,872		9,112
Total held-to-maturity investments		36,712		38,514
Available-for-sale securities:
Auction rate securities		—		2,142
Total available-for-sale investments		—		2,142
Total long-term investments	$	36,712	$	40,656

Held-To-Maturity Securities

As of July 28, 2018 and April 30, 2018, the balance of held-to-maturity securities consisted of state and local government municipal securities, U.S. treasury securities, U.S. government-guaranteed agency securities, U.S. government-sponsored agency debt securities, highly rated corporate bonds, and certificates of deposit. Interest earned from these investments is recorded in interest income.

The amortized cost, gross unrealized gains, gross unrealized losses, and estimated fair value of the held-to-maturity investments as of July 28, 2018 were as follows (in thousands):


	July 28, 2018
			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
Municipal securities	$	16,995	$	8	$	(3)	$	17,000
U.S. government securities		62,323		—		(307)		62,016
Corporate bonds		72,697		1		(53)		72,645
Certificates of deposit		3,000		—		—		3,000
Total held-to-maturity investments	$	155,015	$	9	$	(363)	$	154,661

The amortized cost, gross unrealized gains, gross unrealized losses, and estimated fair value of the held-to-maturity investments as of April 30, 2018 were as follows (in thousands):


	April 30, 2018
			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
Municipal securities	$	37,390	$	9	$	(36)	$	37,363
U.S. government securities		58,976		—		(367)		58,609
Corporate bonds		55,797		2		(71)		55,728
Certificates of deposit		—		—		—		—
Total held-to-maturity investments	$	152,163	$	11	$	(474)	$	151,700

The amortized cost and fair value of the held-to-maturity securities by contractual maturity at July 28, 2018 were as follows (in thousands):


	Cost		Fair Value
Due within one year	$	118,303	$	118,120
Due after one year through five years		36,712		36,541
Total	$	155,015	$	154,661

Available-For-Sale Securities

Auction Rate Securities

As of April 30, 2018, the entire balance of available-for-sale auction rate securities consisted of two investment grade auction rate municipal bonds with maturities ranging from 1 to 16 years. These investments have characteristics similar to short term investments, because at predetermined intervals, generally ranging from 30 to 35 days, there is a new auction process at which the interest rates for these securities are reset to current interest rates. At the end of such period, the Company chooses to roll over its holdings or redeem the investments for cash. A market maker facilitates the redemption of the securities and the underlying issuers are not required to redeem the investment within 365 days. Interest earned from these investments is recorded in interest income.

During the fourth quarter of the fiscal year ended April 30, 2008, the Company began experiencing failed auctions on some of its auction rate securities. A failed auction occurs when a buyer for the securities cannot be obtained and the market maker does not buy the security for its own account. The Company continues to earn interest on the investments that failed to settle at auction, at the maximum contractual rate until the next auction occurs. In the event the Company needs to access funds invested in these auction rate securities, the Company may not be able to liquidate these securities at the fair value recorded on April 30, 2018 until a future auction of these securities is successful or a buyer is found outside of the auction process.

As a result of the failed auctions, the fair values of these securities are estimated utilizing a discounted cash flow analysis as of April 30, 2018. The analysis considers, among other items, the collateralization underlying the security investments, the creditworthiness of the counterparty, the timing of expected future cash flows, and the expectation of the next time the security is expected to have a successful auction.

During the three months ended July 28, 2018, the remaining investment grade auction rate municipal bonds were redeemed at par value.

The amortized cost, gross unrealized gains, gross unrealized losses, and estimated fair value of the auction rate securities as of April 30, 2018, were as follows (in thousands):


			Gross		Gross
	Amortized		Unrealized		Unrealized
	Cost		Gains		Losses		Fair Value
Auction rate securities	$	2,250	$	—	$	(108)	$	2,142
Total available-for-sale investments	$	2,250	$	—	$	(108)	$	2,142