Cash and Investments

The following table presents cash, cash equivalents, and available-for-sale marketable securities for the periods presented (in thousands):



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Market Value
June 30, 2016:
Cash	$	132,287	$	—	$	—		$	132,287
Cash equivalents:
Money market funds	419,858		—		—			419,858
US treasury securities	130,312		1		—			130,313
US agency securities	37,354		—		(5		)	37,349
Marketable securities:
Commercial paper	26,633		29		—			26,662
Certificates of deposit	10,000		5		—			10,005
US treasury securities	942,885		1,048		(11		)	943,922
US agency securities	446,114		400		(4		)	446,510
Corporate debt securities	1,151,409		5,309		(120		)	1,156,598
Municipal securities	8,000		12		—			8,012
Total cash, cash equivalents, and marketable securities	$	3,304,852	$	6,804	$	(140	)	$	3,311,516
December 31, 2015:
Cash	$	180,790	$	—	$	—		$	180,790
Cash equivalents:
Money market funds	276,898		—		—			276,898
Commercial paper	12,048		1		—			12,049
US treasury securities	24,999		1		—			25,000
US agency securities	51,500		—		—			51,500
Marketable securities:
Commercial paper	55,350		47		(23		)	55,374
US treasury securities	874,968		20		(959		)	874,029
US agency securities	606,924		17		(739		)	606,202
Corporate debt securities	1,029,463		96		(2,661		)	1,026,898
Municipal securities	10,636		6		—			10,642
Total cash, cash equivalents, and marketable securities	$	3,123,576	$	188	$	(4,382	)	$	3,119,382

The following table presents unrealized losses on investments by investment category and length of time the investment has been in a continuous unrealized loss position as of the periods presented (in thousands):



	Less than 12 months					12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
June 30, 2016:
Commercial paper	$	994	$	—		$	—	$	—		$	994	$	—
US treasury securities	93,320		(11		)	—		—			93,320		(11		)
US agency securities	60,195		(9		)	—		—			60,195		(9		)
Corporate debt securities	167,217		(110		)	9,677		(10		)	176,894		(120		)
Total	$	321,726	$	(130	)	$	9,677	$	(10	)	$	331,403	$	(140	)
December 31, 2015:
Commercial paper	$	28,482	$	(23	)	$	—	$	—		$	28,482	$	(23	)
US treasury securities	777,237		(959		)	—		—			777,237		(959		)
US agency securities	472,236		(739		)	—		—			472,236		(739		)
Corporate debt securities	943,276		(2,661		)	—		—			943,276		(2,661		)
Total	$	2,221,231	$	(4,382	)	$	—	$	—		$	2,221,231	$	(4,382	)

The following table presents available-for-sale marketable securities by contractual maturity date (in thousands) as of June 30, 2016:



	Amortized Cost		Estimated Fair Market Value
Due in one year or less	$	1,215,357	$	1,215,893
Due after one year through two years	1,009,638		1,012,282
Due after two years through three years	360,046		363,534
Total	$	2,585,041	$	2,591,709