Income Taxes - Additional Information (Detail) - USD ($)	1 Months Ended	9 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Tax year subject to tax examination for U.S. Federal return		As of September 30, 2018, we are no longer subject to examination by U.S. federal tax authorities for years prior to 2014, to examination for any U.S. state taxing authority prior to 2012, or to examination for any foreign jurisdictions prior to 2013. All subsequent periods remain open to examination.
Effective income tax rate, percent		33.40%	35.10%
U.S federal tax rate		21.00%		35.00%
Provisional income tax expense related to repatriation of foreign earnings	$ 3,100,000	$ 200,000
Provisional income tax benefit related to repatriation of foreign earnings		2,900,000
Pre-tax loss recognized		33,500,000
Unrecognized excess tax benefits	$ 14,140,000	$ 0		$ 14,140,000