Goodwill and Other Intangible Assets, Net - Components of Goodwill and Other Intangible Assets, Net (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 410,539	$ 384,697
Intangible assets:
Total intangible assets	151,881	140,593
Total goodwill and intangibles assets	562,420	525,290
Accumulated amortization:
Total accumulated amortization	(63,448)	(56,207)
Goodwill and other intangible assets, net	498,972	469,083
Client Lists [Member]
Intangible assets:
Total intangible assets	143,435	132,637
Accumulated amortization:
Total accumulated amortization	(57,678)	(51,016)
Other Intangible Assets [Member]
Intangible assets:
Total intangible assets	8,446	7,956
Accumulated amortization:
Total accumulated amortization	$ (5,770)	$ (5,191)