Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2012

Marketable Securities

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

	December 31, 2012
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. government securities	$	27,197	$	10	$	(2	)	$	27,205
U.S. government agencies		115,397		85		(16	)		115,466
U.S. corporate notes		91,544		32		(10	)		91,566
U.S. commercial paper		23,082		—		—			23,082
Money market funds		78,646		—		—			78,646
Total	$	335,866	$	127	$	(28	)	$	335,965

	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)	December 31, 2012		December 31, 2011
Cash and cash equivalents	$	86,298	$	38,721
Short-term investments		153,640		196,137
Long-term marketable securities		95,194		—
Restricted cash		833		893
Total	$	335,965	$	235,751

Schedule of net realized gains (losses) on marketable securities

	Year Ended December 31,
(in thousands)	2012		2011			2010
Realized gains	$	9	$	—		$	3
Realized losses		—		(2	)		—
Net realized gains (losses)	$	9	$	(2	)	$	3

Summary of marketable securities with unrealized losses

	In loss position for less than 12 months					In loss position for more than 12 months				Total
(in thousands)	Estimated Fair Value		Estimated Gross Unrealized Losses			Estimated Fair Value		Estimated Gross Unrealized Losses		Estimated Fair Value		Estimated Gross Unrealized Losses
U.S. government securities	$	7,002	$	(2	)	$	—	$	—	$	7,002	$	(2	)
U.S. government agencies		10,499		(16	)		—		—		10,499		(16	)
U.S. corporate notes		34,693		(10	)		—		—		34,693		(10	)
Total	$	52,194	$	(28	)	$	—	$	—	$	52,194	$	(28	)