Goodwill and Other Intangible Assets, Net - Components of Goodwill and Other Intangible Assets, Net (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 442,624	$ 435,231
Intangible assets:
Total intangible assets	150,347	146,669
Total goodwill and intangibles assets	592,971	581,900
Accumulated amortization:
Total accumulated amortization	(62,562)	(55,438)
Goodwill and other intangible assets, net	530,409	526,462
Client Lists [Member]
Intangible assets:
Total intangible assets	143,201	140,187
Accumulated amortization:
Total accumulated amortization	(60,978)	(54,213)
Other Intangible Assets [Member]
Intangible assets:
Total intangible assets	7,146	6,482
Accumulated amortization:
Total accumulated amortization	$ (1,584)	$ (1,225)