Commitments (Details) (USD $)	1 Months Ended	12 Months Ended							12 Months Ended
	May 31, 2011 leases squarefeet	Dec. 31, 2011 leases squarefeet	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 2015 Notes	Sep. 30, 2010 2015 Notes	Sep. 29, 2010 2015 Notes	Dec. 31, 2011 Fan Pier Leases	Dec. 31, 2011 Kendall Square Lease squarefeet Y leases	Dec. 31, 2010 Kendall Square Lease	Dec. 31, 2009 Kendall Square Lease	Dec. 31, 2011 Other Operating Leases
Operating lease
Number of lease terms the entity has the option to extend									2
Length of each lease term the entity has the option to extend (in years)									10
Office space used for operation (in square feet)									120,000
Number of leases	2	2
Area of leased property (in square feet)	1,100,000	1,100,000
Future minimum commitments under facility leases commitments with terms of more than one year
2012		$ 46,865,000							$ 18,260,000			$ 36,455,000
2013		47,778,000							18,260,000			37,942,000
2014		106,067,000						67,206,000	18,260,000			29,025,000
2015		104,202,000						67,206,000	18,260,000			22,678,000
2016		90,077,000						67,206,000	18,260,000			4,611,000
Thereafter		921,575,000						887,211,000	24,346,000			10,018,000
Total minimum lease payments		1,316,564,000						1,088,829,000	115,646,000			140,729,000
Future minimum sublease income
2012		(7,850,000)
2013		(8,424,000)
2014		(8,424,000)
2015		(3,942,000)
Total minimum sublease income		(28,640,000)
Rental expense		49,400,000	46,600,000	39,100,000					11,200,000	11,600,000	11,500,000
Convertible senior subordinated notes (due 2015)		$ 400,000,000	$ 400,000,000		$ 400,000,000	$ 400,000,000	$ 400,000,000