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Fair Value Measurements - Change in Level 3 Fair Values of Contingent Purchase Price Liability (Detail) (Level 3 [Member], USD $) In Thousands, unless otherwise specified			6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Contingent Purchase Price Payable [Member]	Jun. 30, 2012 Contingent Purchase Price Payable [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ (34,254)	$ (30,012)	$ (30,012)	$ (25,325)
Additions from business acquisitions			(4,566)	(2,528)
Payment of contingent purchase price liabilities			1,283	1,982
Change in fair value of contingencies			(904)	111
Change in net present value of contingencies			(55)	(104)
Ending balance	$ (34,254)	$ (30,012)	$ (34,254)	$ (25,864)