Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Schedule Of Income Tax [Line Items]
Effective tax rates	11.70%	(1.60%)	10.70%	0.60%
U.S. federal corporate tax rate			21.00%		35.00%
Tax cuts and jobs act of 2017, Adjustments of provisional income tax expense			$ 9,000,000
Charge relating to change in U.S. federal corporate tax rate			69,000,000
Change in valuation allowance			(69,000,000)
Charge relating to one-time transition tax on unremitted foreign earnings			33,000,000
Net operating loss deferred tax asset, additional charge			9,000,000
Increase in foreign tax credit carryforward	$ 3,000,000
Repeal of deduction limitation for commissions and performance-based compensation.			1,000,000
Maximum [Member]
Schedule Of Income Tax [Line Items]
Global intangible low taxed income provisions and recognized provisional tax expense			1,000,000
Internal Revenue Service [Member]
Schedule Of Income Tax [Line Items]
Change in valuation allowance	(3,000,000)
Deferred tax assets write-down related to performance based compensation	3,000,000
Valuation Allowance,Net Operating Loss [Member]
Schedule Of Income Tax [Line Items]
Change in valuation allowance	$ 3,000,000		$ (9,000,000)