Fair Value Measurements - Change in Level 3 Fair Values of Contingent Purchase Price Liabilities (Detail) - Level 3 [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ (24,817)
Ending balance	(33,709)	$ (24,817)
Contingent Purchase Price Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(24,817)	(33,368)
Additions from business acquisitions	(21,088)	(8,522)
Payment of contingent purchase price payable	11,202	14,364
Change in fair value of contingency	1,342	2,854
Change in net present value of contingency	(348)	(145)
Ending balance	$ (33,709)	$ (24,817)