Goodwill and Identifiable Intangible Assets, Net - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill impairment loss	$ 0	$ 0
Amortization expense of intangible assets acquired	$ 13,100,000	$ 15,000,000	$ 11,100,000