Goodwill and Other Intangible Assets, Net - Components of Goodwill and Other Intangible Assets, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 489,039	$ 487,484
Intangible assets:
Total intangible assets	181,179	180,337
Total goodwill and intangibles assets	670,218	667,821
Accumulated amortization:
Total accumulated amortization	(87,814)	(83,420)
Goodwill and other intangible assets, net	582,404	584,401
Client Lists [Member]
Intangible assets:
Total intangible assets	173,148	172,343
Accumulated amortization:
Total accumulated amortization	(84,646)	(80,560)
Other Intangible Assets [Member]
Intangible assets:
Total intangible assets	8,031	7,994
Accumulated amortization:
Total accumulated amortization	$ (3,168)	$ (2,860)