Fair Value Measurements - Change in Level 3 Fair Values of Contingent Purchase Price Liability (Detail) - Level 3 [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ (24,817)
Ending balance	(22,461)
Contingent Purchase Price Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(24,817)	$ (33,368)
Additions from business acquisitions	(1,206)	(4,186)
Settlement of contingent purchase price liabilities	2,335	3,829
Change in fair value of contingencies	1,263	1,445
Change in net present value of contingencies	(36)	(38)
Ending balance	$ (22,461)	$ (32,318)