Acquisitions (Schedule of Purchase Price Allocation) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	May 15, 2012 Apex Systems	Jul. 31, 2011 HCP	Feb. 28, 2011 Valesta
Business Acquisition [Line Items]
Current assets	$ 10,282	$ 169,803	$ 3,950	$ 6,332
Property and equipment	422	902	123	299
Goodwill	31,486	266,716	14,398	17,088
Identifiable intangible assets	7,463	251,555	1,784	5,679
Other	39	494	13	26
Total assets acquired	49,692	689,470	20,268	29,424
Current liabilities	5,844	77,793	1,070	4,774
Other	1,040	850	49	991
Total liabilities assumed	6,884	78,643	1,119	5,765
Total purchase price	$ 42,808	$ 610,827	$ 19,149	$ 23,659