Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2012

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)
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
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