Goodwill and Other Intangible Assets, Net - Components of Goodwill and Other Intangible Assets, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 487,484	$ 447,685	$ 435,231
Intangible assets:
Total intangible assets	180,337	154,683
Total goodwill and other intangibles assets	667,821	602,368
Accumulated amortization:
Total accumulated amortization	(83,420)	(66,715)
Goodwill and other intangible assets, net	584,401	535,653
Client Lists [Member]
Intangible assets:
Total intangible assets	172,343	147,706
Accumulated amortization:
Total accumulated amortization	(80,560)	(65,037)
Other Intangible Assets [Member]
Intangible assets:
Total intangible assets	7,994	6,977
Accumulated amortization:
Total accumulated amortization	$ (2,860)	$ (1,678)