Goodwill and Other Intangible Assets - Components of Goodwill and Other Intangible Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill	$ 383,107	$ 385,292	$ 379,808	$ 373,117
Other intangible assets (net of accumulated amortization)	5,221	6,072
Goodwill and other intangible assets, Total	$ 388,328	$ 391,364