Available-for-Sale Securities (Tables)

6 Months Ended

Jun. 30, 2012

Available-for-Sale Securities

Schedule of amortized cost and estimated fair values for available-for-sale securities

	June 30, 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	$	30,270	$	1	$	(16	)	$	30,255	$	66,150	$	24	$	—		$	66,174
U.S. government agencies	112,266		4		(74		)	112,196		93,183		9		(17		)	93,175
U.S. corporate notes	60,176		9		(33		)	60,152		2,707		—		(2		)	2,705
U.S. commercial paper	44,993		—		—			44,993		34,973		3		—			34,976
Money market funds	129,891		—		—			129,891		38,721		—		—			38,721
Total	$	377,596	$	14	$	(123	)	$	377,487	$	235,734	$	36	$	(19	)	$	235,751

Schedule of classification of the available-for-sale debt securities

(in thousands)	June 30, 2012		December 31, 2011
Cash and cash equivalents	$	159,053	$	38,721
Short-term investments	134,393		196,137
Long-term marketable securities	83,208		—
Restricted cash	833		893
Total	$	377,487	$	235,751