4.	Cash, Cash Equivalents and Marketable Securities

The following is a summary of cash, cash equivalents and marketable securities as of December 31, 2013, and 2012 (in thousands):

	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
December 31, 2013
Cash and cash equivalents:
Cash	$	1,766	$	-	$	-		$	1,766
Money market funds		20,013		-		-			20,013
U.S. government agency securities		1,343		-		-			1,343
Total cash and cash equivalents		23,122		-		-			23,122
Marketable securities available-for-sale:
U.S. government agency securities		166,285		16		(47	)		166,254
Total marketable securities available-for-sale		166,285		16		(47	)		166,254
Total cash, cash equivalents and marketable securities	$	189,407	$	16	$	(47	)	$	189,376
December 31, 2012
Cash and cash equivalents:
Cash	$	1,542	$	-	$	-		$	1,542
Money market funds		3,140		-		-			3,140
Municipal securities		715		-		-			715
U.S. government agency securities		2,202		-		-			2,202
Total cash and cash equivalents		7,599		-		-			7,599
Marketable securities available-for-sale:
U.S. government agency securities		116,986		46		(1	)		117,031
U.S. treasury securities		500		-		-			500
Total marketable securities available-for-sale		117,486		46		(1	)		117,531
Total cash, cash equivalents and marketable securities	$	125,085	$	46	$	(1	)	$	125,130

The maturities of our marketable securities available-for-sale are as follows (in thousands)

	December 31, 2013
	Amortized Cost		Estimated Fair Value
Mature in one year or less	$	93,691	$	93,701
Mature after one year through two years		72,594		72,553
	$	166,285	$	166,254

We invest in short-term money market funds, U.S. government agency securities, U.S treasury securities and municipal securities.

There were no realized gains or losses from the sale of marketable securities in the years ended December 31, 2013, 2012 and 2011. All of our investments are classified as short-term and available-for-sale, as we may not hold our investments until maturity.