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Segments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
Segments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net sales	$ 122,574	$ 113,500	$ 119,437	$ 113,822	$ 112,340	$ 112,937	$ 109,588	$ 99,082	$ 469,333	$ 433,947	$ 405,232
Gross profit	$ 36,381	$ 27,410	$ 30,204	$ 25,430	$ 27,846	$ 32,830	$ 27,661	$ 15,196	119,425	103,533	123,651
Operating Segments \| Units
Segment Reporting Information [Line Items]
Net sales									434,283	406,331	384,853
Gross profit									121,878	108,214	128,647
Operating Segments \| Parts
Segment Reporting Information [Line Items]
Net sales									35,424	28,456	22,050
Gross profit									17,301	13,215	9,555
Other
Segment Reporting Information [Line Items]
Net sales									(374)	(840)	(1,671)
Gross profit									(19,754)	(17,896)	(14,551)
Inter-segment
Segment Reporting Information [Line Items]
Net sales									28,053	29,385	29,293
Gross profit									$ 985	$ 865	$ 426