Investments

The Company’s marketable securities as of March 31, 2016, were classified as available-for-sale securities, with changes in fair value recognized in Accumulated Other Comprehensive Income ("AOCI"), a component of shareholders’ equity. The Company classifies its marketable securities as cash equivalents, short-term investments or non-current investments based on each instrument's underlying effective maturity date. The following tables summarize available-for-sale marketable securities (in thousands):



Balance as of March 31, 2016:
	Cost			Gross Unrealized Gain			Gross Unrealized Loss			Estimated Fair Value
Short-term investments:
Asset-backed securities	$	53,663		$	5		$	(55	)	$	53,613
Commercial paper	78,721			22			—			78,743
Corporate debt securities	77,742			18			(74		)	77,686
Government agency securities	17,202			4			—			17,206
Other securities	11,626			9			(2		)	11,633
Amounts classified as cash equivalents	(36,387		)	(2		)	—			(36,389		)
Total short-term investments	$	202,567		$	56		$	(131	)	$	202,492
Investments:
Asset-backed securities	$	11,933		$	9		$	(25	)	$	11,917
Corporate debt securities	35,372			79			(15		)	35,436
Government agency securities	11,999			1			—			12,000
Other securities	4,000			8			—			4,008
Total investments	$	63,304		$	97		$	(40	)	$	63,361



Balance as of December 31, 2015:
	Cost			Gross Unrealized Gain		Gross Unrealized Loss			Estimated Fair Value
Short-term investments:
Asset-backed securities	$	52,102		$	—	$	(129	)	$	51,973
Commercial paper	76,711			3		(9		)	76,705
Corporate debt securities	81,777			—		(177		)	81,600
Government agency securities	12,701			—		(17		)	12,684
Other securities	15,122			7		(1		)	15,128
Amounts classified as cash equivalents	(27,943		)	—		—			(27,943		)
Total short-term investments	$	210,470		$	10	$	(333	)	$	210,147
Investments:
Asset-backed securities	$	11,884		$	—	$	(66	)	$	11,818
Corporate debt securities	36,530			3		(119		)	36,414
Government agency securities	11,999			—		(55		)	11,944
Other securities	2,001			—		(2		)	1,999
Total investments	$	62,414		$	3	$	(242	)	$	62,175

Proceeds from the sale of marketable securities were $21.2 million and $13.3 million for the three months ended March 31, 2016 and 2015, respectively. The Company determines gains and losses from sales of marketable securities based on specific identification of the securities sold. Realized gains and losses from sales of marketable securities, all of which are reported as a component of Other income (expense) in the Condensed Consolidated Statements of Operations, were immaterial for the three months ended March 31, 2016 and 2015.

The following table summarizes the fair value of the Company’s marketable securities with unrealized losses at March 31, 2016 and December 31, 2015, and the duration of time that such losses had been unrealized (in thousands):



Balance as of March 31, 2016:
	Less Than 12 months					More than 12 months					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Asset-backed securities	$	45,486	$	(80	)	$	250	$	—		$	45,736	$	(80	)
Corporate debt securities	55,487		(85		)	7,844		(4		)	63,331		(89		)
Government agency securities	2,002		—			—		—			2,002		—
Other securities	1,999		(2		)	—		—			1,999		(2		)
Total	$	104,974	$	(167	)	$	8,094	$	(4	)	$	113,068	$	(171	)



Balance as of December 31, 2015:
	Less Than 12 months					More than 12 months					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Asset-backed securities	$	57,866	$	(192	)	$	5,923	$	(3	)	$	63,789	$	(195	)
Corporate debt securities	101,701		(289		)	8,911		(7		)	110,612		(296		)
Government agency securities	24,628		(72		)	—		—			24,628		(72		)
Commercial Paper	11,374		(9		)	—		—			11,374		(9		)
Other securities	7,496		(3		)	—		—			7,496		(3		)
Total	$	203,065	$	(565	)	$	14,834	$	(10	)	$	217,899	$	(575	)

The Company evaluated marketable securities, which consist of investments in asset-backed securities, corporate debt securities, government agency securities, commercial paper, and other securities as of March 31, 2016, and has determined that there was no indication of other-than-temporary impairments. This determination was based on several factors, including the length of time and extent to which fair value has been less than the cost basis, the financial condition and near-term prospects of the debt issuer, and the Company’s intent and ability to hold the securities for a period of time sufficient to allow for any anticipated recovery in market value.

The following table summarizes the amortized cost and estimated fair value of available-for-sale debt securities at March 31, 2016 and December 31, 2015, by contractual maturity (in thousands):



	March 31, 2016				December 31, 2015
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Mature in one year or less	$	182,069	$	182,035	$	186,311	$	186,118
Mature after one year through three years	112,281		112,340		106,377		106,086
Mature in more than three years	7,908		7,867		8,139		8,061
Total	$	302,258	$	302,242	$	300,827	$	300,265