Financial Instruments

The following is a summary of cash equivalents, available-for-sale securities and equity-type securities as of the end of the periods presented:



	September 29, 2018									March 31, 2018
(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds	$	376,673	$	—	$	—		$	376,673	$	1,291,891	$	—	$	—		$	1,291,891
Financial institution
securities	628,965		15		—			628,980		434,901		—		—			434,901
Non-financial institution
securities	574,630		—		(1,294		)	573,336		326,219		—		(1,376		)	324,843
U.S. government and
agency securities	293,600		22		(337		)	293,285		58,913		1		(272		)	58,642
Foreign government and
agency securities	370,788		3		—			370,791		179,957		—		—			179,957
Mortgage-backed securities	775,806		476		(26,856		)	749,426		866,048		660		(22,311		)	844,397
Asset-backed securities	86,664		9		(1,252		)	85,421		92,751		16		(1,378		)	91,389
Debt mutual funds	101,350		—		(16,424		)	84,926		101,350		—		(11,680		)	89,670
Commercial mortgage-
backed securities	137,767		1		(3,579		)	134,189		156,296		1		(3,427		)	152,870
Marketable equity securities	7,500		—		(799		)	6,701		7,500		726		—			8,226
	$	3,353,743	$	526	$	(50,541	)	$	3,303,728	$	3,515,826	$	1,404	$	(40,444	)	$	3,476,786

Financial institution securities include securities issued or managed by financial institutions in various forms, such as commercial paper and time deposits. Substantially all time deposits were issued by institutions outside the U.S. as of September 29, 2018 and March 31, 2018.

The following tables show the fair values and gross unrealized losses of the Company’s investments, aggregated by investment category, for individual securities that have been in a continuous unrealized loss position for the length of time specified, as of September 29, 2018 and March 31, 2018:



	September 29, 2018
	Less Than 12 Months					12 Months or Greater					Total
(In thousands)	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Non-financial institution securities	$	44,067	$	(748	)	$	19,640	$	(546	)	$	63,707	$	(1,294	)
U.S. government and
agency securities	—		—			15,507		(337		)	15,507		(337		)
Mortgage-backed securities	222,604		(5,996		)	497,433		(20,860		)	720,037		(26,856		)
Asset-backed securities	18,472		(278		)	65,425		(974		)	83,897		(1,252		)
Debt mutual funds	—		—			84,926		(16,424		)	84,926		(16,424		)
Commercial mortgage-
backed securities	44,231		(950		)	88,823		(2,629		)	133,054		(3,579		)
Marketable equity securities	6,701		(799		)	—		—			6,701		(799		)
	$	336,075	$	(8,771	)	$	771,754	$	(41,770	)	$	1,107,829	$	(50,541	)



	March 31, 2018
	Less Than 12 Months					12 Months or Greater					Total
(In thousands)	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Non-financial institution securities	$	69,780	$	(1,146	)	$	8,344	$	(230	)	$	78,124	$	(1,376	)
U.S. government and
agency securities	13,471		(176		)	9,176		(96		)	22,647		(272		)
Mortgage-backed securities	510,988		(11,048		)	299,663		(11,263		)	810,651		(22,311		)
Asset-backed securities	57,128		(876		)	32,696		(502		)	89,824		(1,378		)
Debt mutual funds	—		—			89,670		(11,680		)	89,670		(11,680		)
Commercial mortgage-
backed securities	95,435		(1,760		)	56,051		(1,667		)	151,486		(3,427		)
	$	746,802	$	(15,006	)	$	495,600	$	(25,438	)	$	1,242,402	$	(40,444	)

As of September 29, 2018, the gross unrealized losses that had been outstanding for less than twelve months were primarily related to mortgage-backed securities due to the general rising of the interest-rate environment, although the percentage of such losses to the total estimated fair value of the mortgage-backed securities was relatively insignificant. The gross unrealized losses that had been outstanding for more than twelve months were primarily related to debt mutual funds and mortgage-backed securities, which were primarily due to the general rising of the interest-rate environment and foreign currency movement.

Starting April 1, 2018, the Company records the change in the fair value of its investment in debt mutual funds and marketable equity securities as part of its interest and other income, net. This change in fair value was a net decrease of $73 thousand and $6.3 million for the three and six months ended September 29, 2018, respectively, and resulted in an expense within interest and other income, net for the period.

The Company reviewed the investment portfolio and determined that the gross unrealized losses on these investments as of September 29, 2018 and March 31, 2018 were temporary in nature as evidenced by the fluctuations in the gross unrealized losses within the investment categories. These investments are highly rated by the credit rating agencies, there have been no defaults on any of these securities and the company has received interest payments as they become due. Therefore, the Company believes that it will be able to collect both principal and interest amount due to the Company. Additionally, in the past several years a portion of the Company's investment in the mortgage-backed securities was redeemed or prepaid by the debtors at par. Furthermore, the aggregate of individual unrealized losses that had been outstanding for twelve months or more was not significant as of September 29, 2018 and March 31, 2018. The Company neither intends to sell these investments nor concludes that it is more-likely-than-not that it will have to sell them until recovery of their carrying values.

The amortized cost and estimated fair value of marketable debt securities (financial institution securities, non-financial institution securities, U.S. and foreign government and agency securities, asset-backed securities, mortgage-backed securities and commercial mortgage-backed securities), by contractual maturity, are shown in the table below. Actual maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations without call or prepayment penalties.



	September 29, 2018
(In thousands)	Amortized Cost		Estimated Fair Value
Due in one year or less	$	1,825,385	$	1,825,113
Due after one year through five years	162,134		158,928
Due after five years through ten years	139,922		135,283
Due after ten years	740,779		716,104
	$	2,868,220	$	2,835,428

As of September 29, 2018, $1.01 billion of marketable debt securities with contractual maturities of greater than one year were classified as short-term investments. Additionally, the above table does not include investments in money market, debt mutual funds and marketable equity securities because these investments do not have specific contractual maturities.

Certain information related to available-for-sale securities is as follows:



	Three Months Ended						Six Months Ended
(In thousands)	September 29, 2018			September 30, 2017			September 29, 2018			September 30, 2017
Proceeds from sale of available-for-sale securities	$	7		$	149,497		$	903		$	269,419
Gross realized gains on sale of available-for-sale securities	$	—		$	519		$	96		$	1,351
Gross realized losses on sale of available-for-sale securities	(1		)	(209		)	(48		)	(595		)
Net realized gains (losses) on sale of available-for-sale securities	$	(1	)	$	310		$	48		$	756
Amortization of premiums on available-for-sale securities	$	2,645		$	4,691		$	5,136		$	10,213

The cost of securities matured or sold is based on the specific identification method.