Available-for-Sale Securities (Tables)

9 Months Ended

Sep. 30, 2012

Available-for-Sale Securities

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

	September 30, 2012
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. government securities	$	30,233	$	9	$	—		$	30,242
U.S. government agencies	107,073		69		(1		)	107,141
U.S. corporate notes	98,599		45		(7		)	98,637
U.S. commercial paper	37,336		1		—			37,337
Money market funds	85,634		—		—			85,634
Total	$	358,875	$	124	$	(8	)	$	358,991

	December 31, 2011
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. government securities	$	66,150	$	24	$	—		$	66,174
U.S. government agencies	93,183		9		(17		)	93,175
U.S. corporate notes	2,707		—		(2		)	2,705
U.S. commercial paper	34,973		3		—			34,976
Money market funds	38,721		—		—			38,721
Total	$	235,734	$	36	$	(19	)	$	235,751

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

(in thousands)	September 30, 2012		December 31, 2011
Cash and cash equivalents	$	107,987	$	38,721
Short-term investments	161,209		196,137
Long-term marketable securities	88,962		—
Restricted cash	833		893
Total	$	358,991	$	235,751