Marketable Securities

3 Months Ended

Mar. 31, 2012

Marketable Securities

Marketable Securities

4. Marketable Securities

Available-for-sale money market funds and debt securities were recorded in cash equivalents or marketable securities in the Company’s consolidated balance sheets at their estimated fair value based on prices obtained from commercial pricing services. The Company’s marketable securities were as follows:

	March 31, 2012										December 31, 2011
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value			Amortized Cost			Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. government securities	$	61,028	$	5	$	(2	)	$	61,031		$	66,150		$	24	$	—		$	66,174
U.S. government agencies	82,942		2		(15		)	82,929			93,183			9		(17		)	93,175
U.S. corporate notes	550		—		—			550			2,707			—		(2		)	2,705
U.S. commercial paper	45,736		1		—			45,737			34,973			3		—			34,976
Money market funds	6,213		—		—			6,213			38,721			—		—			38,721
Total	196,469		8		(17		)	196,460			235,734			36		(19		)	235,751
Less amounts classified as cash equivalents	(9,713)		—		—			(9,713		)	(38,721		)	—		—			(38,721		)
Less amounts classified as restricted cash	(893)		—		—			(893		)	(893		)	—		—			(893		)
Amounts classified as marketable securities	$	185,863	$	8	$	(17	)	$	185,854		$	196,120		$	36	$	(19	)	$	196,137

At March 31, 2012, all of the marketable securities have contractual maturities within twelve months and the average duration of marketable securities was approximately five months. The Company does not intend to sell the investments which are in an unrealized loss position and it is unlikely that the Company will be required to sell the investments before recovery of their amortized cost basis, which may be maturity. The Company has determined that the gross unrealized losses on its marketable securities at March 31, 2012, were temporary in nature. All marketable securities with unrealized losses have been in a loss position for less than twelve months.