Geographic Information (Tables)

12 Months Ended

Dec. 31, 2017

Segments Geographical Areas [Abstract]

Geographical Information Attributable to Net Sales

	Years ended December 31,
	2015		2016		2017
	(in thousands)
Net sales - point of destination:
United States	$	103,737	$	98,526	$	103,646
Canada		2,352		7,515		5,353
Other		2,905		2,879		3,036
Total	$	108,994	$	108,920	$	112,035