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
Income Tax Contingency [Line Items]
Effective income tax percentage			21.00%		35.00%
U.S. statutory tax rate, including state and local taxes			25.90%		39.00%
Income tax expense	$ (900,000)	$ 900,000	$ 5,800,000	$ 3,800,000
Unrecognized tax benefits	1,300,000		1,300,000		$ 1,500,000
Accrued Interest included in unrecognized tax benefits	200,000		200,000		$ 400,000
Unrecognized tax benefits if recognized would impact on effective income tax rate	1,300,000		$ 1,300,000
Income tax examination description			With a few exceptions, we are no longer subject to U.S. federal, state and local, or non-U.S. income tax examinations by tax authorities for years before 2014.
Internal Revenue Service [Member]
Income Tax Contingency [Line Items]
Increase in includible untaxed foreign earnings	16,200,000
Increase in tax expense	5,700,000
Net operating loss carryover	16,200,000		$ 16,200,000
Impact to tax expense	$ 0