Fair Value Measurements - Change in Level 3 Fair Values of Contingent Purchase Price Liability (Detail) - Level 3 [Member] - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ (33,368)
Ending balance	(24,778)
Contingent Purchase Price Payable [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(33,368)	$ (25,196)
Additions from business acquisitions	(4,186)	(13,953)
Settlement of contingent purchase price liabilities	9,816	2,285
Change in fair value of contingencies	3,075	3,592
Change in net present value of contingencies	(115)	(97)
Ending balance	$ (24,778)	$ (33,369)