Fair Value Measurements - Change in Level 3 Fair Values of Contingent Purchase Price Liability (Detail) (Level 3 [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Ending balance	$ (33,368)	$ (25,196)
Contingent Purchase Price Payable [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(25,196)	(30,012)
Additions from business acquisitions	(19,353)	(5,487)
Payment of contingent purchase price payable	5,230	11,511
Change in fair value of contingency	6,080	(1,102)
Change in net present value of contingency	(129)	(106)
Ending balance	$ 33,368	$ (25,196)