4. MARKETABLE SECURITIES

Marketable securities classified as available-for-sale consisted of the following (in thousands):


	March 31, 2013
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Corporate bonds	$	67,256	$	172	$	(25	)	$	67,403
Asset-backed securities		33,578		42		(4	)		33,616
Commercial paper		32,957		11		-			32,968
Government and agency securities		27,972		37		(28	)		27,981
Mortgage-backed securities		14,481		56		(14	)		14,523
Municipal bonds		6,421		10		(1	)		6,430
Certificates of deposit		750		—		—			750

	$	183,415	$	328	$	(72	)	$	183,671


	December 31, 2012
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Corporate bonds	$	49,545	$	203	$	(4	)	$	49,744
Government and agency securities		23,431		43		(27	)		23,447
Asset-backed securities		23,079		70		—			23,149
Mortgage-backed securities		12,064		40		(15	)		12,089
Commercial paper		1,200		—		—			1,200
Municipal bonds		6,273		13		—			6,286
Certificates of deposit		1,003		1		—			1,004
Floating rate notes		1,266		2		—			1,268

	$	117,861	$	372	$	(46	)	$	118,187

The following table summarizes the amortized cost and fair value of the Company’s marketable securities, classified by stated maturity as of March 31, 2013 and December 31, 2012 (in thousands):


	March 31, 2013				December 31, 2012
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Marketable securities
Due in 1 year or less	$	100,261	$	100,379	$	53,761	$	53,852
Due in 1-2 years		47,695		47,795		36,510		36,694
Due in 2-3 years		13,397		13,387		11,847		11,856
Due in 3-4 years		4,546		4,544		744		746
Due in 4-9 years		5,653		5,680		5,158		5,179
Due in 9-20 years		2,262		2,269		1,032		1,040
Due in 20-33 years		9,601		9,617		8,809		8,820

	$	183,415	$	183,671	$	117,861	$	118,187

Marketable securities classified as available-for-sale are carried at fair value as of March 31, 2013 and December 31, 2012. Realized gains and losses from sales and maturities of marketable securities were not significant in the periods presented.

The aggregate fair value of available-for-sale securities with unrealized losses as of March 31, 2013 was $52.1 million. Gross unrealized losses on available-for-sale securities as of March 31, 2013 were insignificant and the Company believes the gross unrealized losses are temporary. In determining that the decline in fair value of these securities was temporary, the Company considered the length of time each security was in an unrealized loss position and the extent to which the fair value was less than cost. The aggregate fair value and unrealized loss of available-for-sale securities which had been in a continuous loss position for more than 12 months was $1.3 million and $26,000 as of March 31, 2013, respectively. In addition, the Company does not intend to sell these securities and it is more likely than not that the Company will not be required to sell these securities before the recovery of their amortized cost basis.