Basis of Presentation and Summary Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Significant Accounting Policies [Line Items]
Percentage of total annual net sales in the third and fourth quarters					60.00%	61.00%
Impairment of goodwill	$ 2,205		$ 2,205
Restructuring charges	552	$ 272	1,353	$ 526
Employee Severance
Schedule Of Significant Accounting Policies [Line Items]
Restructuring charges	600		1,400
Accrued restructuring change	800		800
Receivables Purchase Agreement
Schedule Of Significant Accounting Policies [Line Items]
Sale of receivable	20,700	23,600	59,400	62,800
Sale of receivable, outstanding	13,600		13,600
Receivables Purchase Agreement | Selling, General and Administrative Expenses
Schedule Of Significant Accounting Policies [Line Items]
Charge related to sale of receivables	$ 111	$ 88	$ 300	$ 218