Contingent Consideration Liability (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Business Acquisition, Contingent Consideration [Line Items]
Beginning Balance	$ 72,046	$ 77,719
Payment of contingent considerations on acquisitions	(12,260)	(8,316)
(Income) expense from fair value adjustments	(7,699)	858
Ending Balance	$ 52,087	$ 70,261