Contingent Consideration Liability Measured at Fair Value on Recurring Basis using Significant Unobservable (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Business Acquisition, Contingent Consideration [Line Items]
Beginning balance	$ 72,046	$ 77,719
Payment of contingent consideration on acquisitions	(17,371)	(8,316)
Expense(Income) from fair value adjustments	(3,512)	2,643
Ending balance	$ 51,163	$ 72,046