Goodwill and Other Intangible Assets (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Impairment of goodwill			$ 0	$ 0
Amortization expense for intangible assets	$ 12,200,000	$ 12,200,000	$ 24,400,000	$ 24,200,000