Goodwill and Other Intangible Assets, Net - Components of Goodwill and Other Intangible Assets, Net (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Intangible assets:
Total intangible assets	$ 144,709	$ 143,488
Total goodwill and intangible assets	527,969	518,610
Accumulated amortization:
Total accumulated amortization	(57,060)	(49,039)
Goodwill and other intangible assets, net	470,909	469,571
Client lists [Member]
Intangible assets:
Total intangible assets	136,412	134,987
Accumulated amortization:
Total accumulated amortization	(51,793)	(44,293)
Other intangible assets [Member]
Intangible assets:
Total intangible assets	8,297	8,501
Accumulated amortization:
Total accumulated amortization	(5,267)	(4,746)
Indefinite-lived Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 383,260	$ 375,122