Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Net sales	$ 91,057	$ 88,132	$ 281,368	$ 278,413	[1]
Remaining performance obligation	3,000		3,000
Change In Contract With Customer Liability [Roll Forward]
Balance, beginning of period	748	956	1,084	1,096
Cash additions	354	99	1,347	1,159
Revenue recognition	(227)	(185)	(1,556)	(1,385)
Balance, end of period	875	870	875	870
United States
Disaggregation of Revenue [Line Items]
Net sales	81,423	74,597	250,502	242,365
Canada
Disaggregation of Revenue [Line Items]
Net sales	4,306	6,984	13,372	17,701
All other
Disaggregation of Revenue [Line Items]
Net sales	5,328	6,551	17,494	18,347
Product sales
Disaggregation of Revenue [Line Items]
Net sales	88,068	84,816	269,288	266,057
Extended warranties and services
Disaggregation of Revenue [Line Items]
Net sales	1,611	1,927	6,830	7,789
Other
Disaggregation of Revenue [Line Items]
Net sales	1,378	$ 1,389	5,250	$ 4,567
Retail Orders
Disaggregation of Revenue [Line Items]
Remaining performance obligation	2,400		2,400
Direct Orders
Disaggregation of Revenue [Line Items]
Remaining performance obligation	$ 600		$ 600

[1] See Note 2.