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Fair Value Measurements (Details 1) (Level 3 [Member], USD $) In Thousands, unless otherwise specified			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Contingent Purchase Price Payable [Member]	Mar. 31, 2012 Contingent Purchase Price Payable [Member]
Change in fair values of assets and liabilities identified as level 3
Beginning balance	$ (29,951)	$ (30,012)	$ (30,012)	$ (25,325)
Additions from business acquisitions				(1,088)
Payment of contingent purchase price liabilities			980	1,692
Change in fair value of contingencies			(887)	259
Change in net present value of contingencies			(32)	(54)
Ending balance	$ (29,951)	$ (30,012)	$ (29,951)	$ (24,516)