Fair Value Measurements - Change in Level 3 Fair Values of Contingent Purchase Price Liability (Detail) (Level 3 [Member], USD $) In Thousands, unless otherwise specified			3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Contingent Purchase Price Payable [Member]	Mar. 31, 2013 Contingent Purchase Price Payable [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ (32,953)	$ (25,196)	$ (25,196)	$ (30,012)
Additions from business acquisitions			(10,191)
Payment of contingent purchase price liabilities			1,494	980
Change in fair value of contingencies			959	(887)
Change in net present value of contingencies			(19)	(32)
Ending balance	$ (32,953)	$ (25,196)	$ (32,953)	$ (29,951)