Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2011

Marketable Securities

Summary of cash, cash equivalents and marketable securities

		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
		(in thousands)
September 30, 2011
Cash and cash equivalents:
	Cash and money market funds	$	348,199	$	—	$	—		$	348,199
	U.S. Treasury securities		7,788		—		—			7,788
	Government-sponsored enterprise securities		186,586		1		(29	)		186,558
Total cash and cash equivalents		$	542,573	$	1	$	(29	)	$	542,545
Marketable securities:
	Government-sponsored enterprise securities (due within 1 year)	$	116,144	$	6	$	(10	)	$	116,140
Total marketable securities		$	116,144	$	6	$	(10	)	$	116,140
Total cash, cash equivalents and marketable securities		$	658,717	$	7	$	(39	)	$	658,685
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