Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2013

Cash and Cash Equivalents [Abstract]

Summary of cash, cash equivalents and marketable securities

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 March 31, 2013
Cash and cash equivalents:
Cash and money market funds	$	340,511	$	—	$	—		$	340,511
Government-sponsored enterprise securities	38,584		4		—			38,588
Total cash and cash equivalents	$	379,095	$	4	$	—		$	379,099
Marketable securities:
U.S. Treasury securities (due within 1 year)	$	13,204	$	1	$	—		$	13,205
Government-sponsored enterprise securities (due within 1 year)	550,418		72		(12		)	550,478
Commercial paper (due within 1 year)	216,776		166		—			216,942
Corporate debt securities (due within 1 year)	59,666		3		(19		)	59,650
Corporate debt securities (due after 1 year through 5 years)	19,988		1		(9		)	19,980
Total marketable securities	$	860,052	$	243	$	(40	)	$	860,255
Total cash, cash equivalents and marketable securities	$	1,239,147	$	247	$	(40	)	$	1,239,354
As of December 31, 2012
Cash and cash equivalents:
Cash and money market funds	$	489,407	$	—	$	—		$	489,407
Total cash and cash equivalents	$	489,407	$	—	$	—		$	489,407
Marketable securities:
U.S. Treasury securities (due within 1 year)	$	111,350	$	2	$	(2	)	$	111,350
Government-sponsored enterprise securities (due within 1 year)	440,181		49		(5		)	440,225
Commercial paper (due within 1 year)	225,294		155		—			225,449
Corporate debt securities (due within 1 year)	15,429		1		(1		)	15,429
Corporate debt securities (due after 1 year through 5 years)	39,358		10		(13		)	39,355
Total marketable securities	$	831,612	$	217	$	(21	)	$	831,808
Total cash, cash equivalents and marketable securities	$	1,321,019	$	217	$	(21	)	$	1,321,215