Goodwill and Other Intangible Assets (Schedule of Goodwill and Other Intangible Assets) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended											6 Months Ended	12 Months Ended
	Jun. 30, 2012	Jun. 25, 2011	Jun. 30, 2012	Jun. 25, 2011	Dec. 31, 2011	Jun. 30, 2012 Backlog [Member]	Dec. 31, 2011 Backlog [Member]	Jun. 30, 2012 Client Relationships [Member]	Dec. 31, 2011 Client Relationships [Member]	Jun. 30, 2012 Trademarks and Trade Names [Member]	Dec. 31, 2011 Trademarks and Trade Names [Member]	Jun. 30, 2012 Other Identifiable Intangible Assets [Member]	Dec. 31, 2011 Other Identifiable Intangible Assets [Member]	Jun. 30, 2012 Research Models [Member]	Dec. 31, 2011 Research Models [Member]
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill, Gross Carrying Amount	$ 1,212,924		$ 1,212,924		$ 1,214,285
Goodwill, Accumulated Amortization & Impairment Loss	(1,016,700)		(1,016,700)		(1,016,724)
Other intangible assets
Other intangible assets not subject to amortization, Gross Carrying Amount														3,438	3,438
Amortization of Intangible assets	4,411	5,797	8,906	11,177										0	0
Other intangible assets subject to amortization, Gross Carrying Amount						2,833	2,856	298,774	298,813	5,017	5,022	5,395	5,415
Other intangible assets, Gross Carrying Amount	315,457		315,457		315,544
Other intangible assets subject to amortization, Accumulated Amortization & Impairment Loss	$ (230,886)		$ (230,886)		$ (222,107)	$ (2,299)	$ (2,253)	$ (219,456)	$ (210,816)	$ (4,751)	$ (4,706)	$ (4,380)	$ (4,332)