Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2011

Marketable Securities

Summary of cash, cash equivalents and marketable securities

		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
		(in thousands)
June 30, 2011
Cash and cash equivalents
	Cash and money market funds	$	422,289	$	—	$	—		$	422,289
	Government-sponsored enterprise securities		35,905		1		—			35,906
Total cash and cash equivalents		$	458,194	$	1	$	—		$	458,195
Marketable securities
	U.S. Treasury securities (due within 1 year)	$	9,546	$	1	$	—		$	9,547
	Government-sponsored enterprise securities (due within 1 year)		125,739		10		—			125,749
Total marketable securities		$	135,285	$	11	$	—		$	135,296
Total cash, cash equivalents and marketable securities		$	593,479	$	12	$	—		$	593,491
December 31, 2010
Cash and cash equivalents
	Cash and money market funds	$	193,845	$	—	$	—		$	193,845
	U.S. Treasury securities		4,770		—		—			4,770
	Government-sponsored enterprise securities		44,587		1		(6	)		44,582
Total cash and cash equivalents		$	243,202	$	1	$	(6	)	$	243,197
Marketable securities
	U.S. Treasury securities (due within 1 year)	$	103,230	$	1	$	(11	)	$	103,220
	Government-sponsored enterprise securities (due within 1 year)		684,969		87		(62	)		684,994
Total marketable securities		$	788,199	$	88	$	(73	)	$	788,214
Total cash, cash equivalents and marketable securities		$	1,031,401	$	89	$	(79	)	$	1,031,411