A summary of the Company's cash, cash equivalents and marketable securities is shown below:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value

	(in thousands)
As of June 30, 2012
Cash and cash equivalents:
Cash and money market funds	$	272,840	$	—	$	—		$	272,840
U.S. Treasury securities		181,234		—		(13	)		181,221

Total cash and cash equivalents	$	454,074	$	—	$	(13	)	$	454,061

Marketable securities:
U.S. Treasury securities (due within 1 year)	$	114,060	$	2	$	(7	)	$	114,055
Government-sponsored enterprise securities (due within 1 year)		371,170		15		(27	)		371,158
Commercial paper (due within 1 year)		229,243		192		—			229,435
Corporate debt securities (due within 1 year)		54,641		—		(16	)		54,625

Total marketable securities	$	769,114	$	209	$	(50	)	$	769,273

Total cash, cash equivalents and marketable securities	$	1,223,188	$	209	$	(63	)	$	1,223,334

As of December 31, 2011
Cash and cash equivalents:
Cash and money market funds	$	362,035	$	—	$	—		$	362,035
Government-sponsored enterprise securities		113,302		—		(17	)		113,285

Total cash and cash equivalents	$	475,337	$	—	$	(17	)	$	475,320

Marketable securities:
U.S. Treasury securities (due within 1 year)	$	22,105	$	2	$	—		$	22,107
Government-sponsored enterprise securities (due within 1 year)		471,589		8		(102	)		471,495

Total marketable securities	$	493,694	$	10	$	(102	)	$	493,602

Total cash, cash equivalents and marketable securities	$	969,031	$	10	$	(119	)	$	968,922

Alios' $56.0 million and $51.9 million of cash and money market funds as of June 30, 2012 and December 31, 2011, respectively, recorded on the Company's condensed consolidated balance sheets in "Restricted cash and cash equivalents (Alios)," are not included in the above table.