Financial Instruments

Cash, Cash Equivalents and Marketable Securities

The following tables summarize our cash and available-for-sale securities by significant investment category.



	September 25, 2015
(In thousands)	Cost		Unrealized Gains		Unrealized Losses			Fair Value		Cash and Cash Equivalents		Short-Term Marketable Securities		Long-Term Marketable Securities

Cash	$	91,530	$	—	$	—		$	91,530	$	91,530	$	—	$	—

Available-for-sale:
Level 1:
Money market funds	1,836,269		—		—			1,836,269		1,836,269		—		—
U.S. treasury securities	950,631		12,176		(58		)	962,749		6,801		46,846		909,102
Subtotal	2,786,900		12,176		(58		)	2,799,018		1,843,070		46,846		909,102

Level 2:
U.S. agency securities	29,536		20		(16		)	29,540		—		5,953		23,587
Non-U.S. government securities	44,217		27		(15		)	44,229		—		7,104		37,125
Municipal bonds	4,272		1		(1		)	4,272		—		2,001		2,271
Corporate debt securities	1,659,993		2,249		(5,526		)	1,656,716		250		123,858		1,532,608
Subtotal	1,738,018		2,297		(5,558		)	1,734,757		250		138,916		1,595,591
Total	$	4,616,448	$	14,473	$	(5,616	)	$	4,625,305	$	1,934,850	$	185,762	$	2,504,693



	December 31, 2014
(In thousands)	Cost		Unrealized Gains		Unrealized Losses			Fair Value		Cash and Cash Equivalents		Short-Term Marketable Securities		Long-Term Marketable Securities

Cash	$	57,505	$	—	$	—		$	57,505	$	57,505	$	—	$	—

Available-for-sale:
Level 1:
Money market funds	2,366,799		—		—			2,366,799		2,366,799		—		—
U.S. treasury securities	1,338,162		12,721		(2,302		)	1,348,581		500		38,938		1,309,143
Subtotal	3,704,961		12,721		(2,302		)	3,715,380		2,367,299		38,938		1,309,143

Level 2:
U.S. agency securities	21,186		12		(7		)	21,191		—		11,748		9,443
Non-U.S. government securities	31,281		2		(17		)	31,266		—		19,459		11,807
Municipal bonds	2,000		2		—			2,002		—		1,001		1,001
Corporate debt securities	693,638		362		(1,115		)	692,885		1,563		80,373		610,949
Subtotal	748,105		378		(1,139		)	747,344		1,563		112,581		633,200
Total	$	4,510,571	$	13,099	$	(3,441	)	$	4,520,229	$	2,426,367	$	151,519	$	1,942,343

As of September 25, 2015, we had cost method investments of approximately $24.6 million. These investments are included within Other assets, net on our consolidated balance sheets. The investments are non-marketable equity investments in privately held companies in which we have less than a 20% interest and no significant influence over the investee's operations. We report these investments at cost, except when investments are found to be other-than-temporarily impaired after an impairment review. We did not recognize any impairment losses for 2015 or 2014.

The adjusted cost and estimated fair value of marketable debt securities (corporate debt securities, municipal bonds, U.S. and foreign government securities, and U.S. treasury securities) as of September 25, 2015, by contractual maturity, are shown 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 25, 2015
(In thousands)	Cost		Estimated Fair Value
Due in one year or less	$	192,761	$	192,813
Due after one year through five years	2,086,510		2,087,321
Due between six and ten years	409,378		417,372
	$	2,688,649	$	2,697,506

As of September 25, 2015, we had $1.1 billion in available-for-sale securities in our investment portfolio that were in a continuous unrealized loss position for less than 12 months with a gross unrealized loss of $5.6 million. As of December 31, 2014, we had $1.1 billion in available-for-sale securities in our investment portfolio that were in a continuous unrealized loss position for less than 12 months with a gross unrealized loss of $3.4 million.

We concluded that the declines in market value of our available-for-sale securities investment portfolio were temporary in nature and did not consider any of our investments to be other-than-temporarily impaired.