Acquisitions - Additions to Goodwill, Client Lists and Other Intangible Assets Resulting from Acquisitions and Contingent Consideration Earned on Prior Period Acquisitions (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 32,094	$ 7,378
Client Lists [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired	11,606	3,499
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired	$ 559	$ 166