Income Taxes -Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Income Tax Disclosure [Abstract]
Decrease of deferred tax assets	$ 301.0
Decrease in valuation allowance	301.0
Additional income tax expense or benefit	0.0
Provisional amount recorded related to mandatory deemed repatriation of foreign earnings	$ 0.0