Segment Information - Net Sales to Unaffiliated Customers by Geographic Area (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales, Total	$ 121,333	$ 108,556	$ 106,625
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales, Total	89,340	77,982	79,535
United Kingdom [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales, Total	14,391	12,544	9,944
Other International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales, Total	$ 17,602	$ 18,030	$ 17,146