Available-for-Sale Securities

3 Months Ended

Mar. 31, 2012

3. Available-for-Sale Securities

The following is a summary of available-for-sale securities included in cash and cash equivalents and marketable securities as of March 31, 2012 and December 31, 2011 (in thousands):


	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
March 31, 2012:
Certificates of deposit and money market funds	$	17,782	$	—	$	—		$	17,782
U.S. government agency securities		38,999		3		(4	)		38,998
Corporate debt securities		48,129		2		(4	)		48,127

Total	$	104,910	$	5	$	(8	)	$	104,907

December 31, 2011:
Certificates of deposit and money market funds	$	25,243	$	—	$	—		$	25,243
U.S. Government agency securities		28,501		—		(6	)		28,495
Corporate debt securities		58,577		9		(6	)		58,580

Total	$	112,321	$	9	$	(12	)	$	112,318

There were no realized gains or losses from the sale of marketable securities in the three months ended March 31, 2012 and 2011. As of March 31, 2012 and December 31, 2011, all of our investments have a stated maturity date that is within two years of the current balance sheet date. All of our investments are classified as short-term and available-for-sale, as we may not hold our investments until maturity.