Income Taxes - Additional Information (Detail) - USD ($)		3 Months Ended		12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2019	Sep. 30, 2018
Income Tax Contingency [Line Items]
U.S. corporate statutory tax rate		35.00%	35.00%
Enacted tax rate		21.00%
Provisional income tax expense		$ 27,000,000
Provisional deferred tax liability		$ 4,000,000
One time transition tax for accumulated foreign earnings imposed tax rate on cash and cash equivalents		15.50%
One time transition tax for accumulated foreign earnings imposed tax rate on illiquid assets		8.00%
Income tax impact to transition tax		$ 0
Income tax liability		0
Income tax expense		$ 52,000,000	$ 17,000,000
Blended federal statutory income tax rate		24.50%
Income withholding taxes and foreign losses uncertain tax positions		$ 0	$ 0
Maximum
Income Tax Contingency [Line Items]
Reasonably possible decrease in gross unrecognized tax benefits from ongoing audits and settlement		$ 3,000,000
Scenario, Forecast
Income Tax Contingency [Line Items]
U.S. corporate statutory tax rate				21.00%	24.50%
Subsequent Event
Income Tax Contingency [Line Items]
U.S. corporate statutory tax rate	21.00%