Goodwill and Other Intangible Assets - Components of Goodwill and Other Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill	$ 385,292	$ 373,117	$ 320,761	$ 335,402
Other intangible assets (net of accumulated amortization)	6,072	8,907
Goodwill and other intangible assets, Total	$ 391,364	$ 382,024