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, 2013	Sep. 30, 2012
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 8,138	$ 14,728
Client lists [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets	3,609	10,243
Other intangible assets [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets	$ 171	$ 373