Goodwill and Other Intangible Assets, Net - Components of Goodwill and Other Intangible Assets, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 448,611	$ 447,685
Intangible assets:
Total intangible assets	156,908	154,683
Total goodwill and intangibles assets	605,519	602,368
Accumulated amortization:
Total accumulated amortization	(70,633)	(66,715)
Goodwill and other intangible assets, net	534,886	535,653
Client Lists [Member]
Intangible assets:
Total intangible assets	149,899	147,706
Accumulated amortization:
Total accumulated amortization	(68,714)	(65,037)
Other Intangible Assets [Member]
Intangible assets:
Total intangible assets	7,009	6,977
Accumulated amortization:
Total accumulated amortization	$ (1,919)	$ (1,678)