Acquisitions - Summary of Purchase Price Allocations Initially Recorded on Consolidated Balance Sheet for all Acquisitions (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Loans At Acquisition Date [Line Items]
Goodwill	$ 502,015	$ 471,684
Series of Individually Immaterial Business Acquisitions [Member]
Loans At Acquisition Date [Line Items]
Net liabilities	(14,195)
Goodwill	34,137
Intangible assets	16,944
Deferred tax liability	(1,352)
Total purchase price consideration	$ 35,534