Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2012

Marketable Securities

Schedule of estimated fair values of available-for-sale money market funds and debt securities

	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