Segment Reporting (Schedule of Information Relating to Segments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information
Net sales	$ 2,796,166	$ 2,371,482	$ 2,475,807
Operating profit (loss)	222,934	200,210	198,788
Total assets	2,298,031	1,862,595	1,243,893
Expenditures for long-lived assets	299,259	469,188	268,439
Depreciation and amortization	97,980	75,358	67,526
Purchase of long-lived assets as part of business acquisition	299,300	395,600	150,900
OEM Segment
Segment Reporting Information
Net sales	2,167,911	2,091,901	2,242,616
Aftermarket Segment
Segment Reporting Information
Net sales	628,255	279,581	233,191
Corporate and Other
Segment Reporting Information
Operating profit (loss)	0	0	0
Total assets	122,653	99,008	79,863
Depreciation and amortization	$ 0	$ 0	$ 0
Net sales | OEM Segment
Segment Reporting Information
Consolidated risk, percentage	78.00%	88.00%	91.00%
Net sales | Aftermarket Segment
Segment Reporting Information
Consolidated risk, percentage	22.00%	12.00%	9.00%
Customer Concentration Risk | Net sales | Thor Industries, Inc.
Segment Reporting Information
Consolidated risk, percentage	21.00%	27.00%	31.00%
Customer Concentration Risk | Net sales | Berkshire Hathaway Inc.
Segment Reporting Information
Consolidated risk, percentage	19.00%	21.00%	23.00%
Operating Segments
Segment Reporting Information
Net sales	$ 2,796,166	$ 2,371,482	$ 2,475,807
Operating profit (loss)	222,934	200,210	198,788
Total assets	2,175,378	1,763,587	1,164,030
Expenditures for long-lived assets	299,259	469,188	268,439
Depreciation and amortization	97,980	75,358	67,526
Operating Segments | OEM Segment
Segment Reporting Information
Net sales	2,167,911	2,091,901	2,242,616
Operating profit (loss)	156,092	165,290	167,459
Total assets	1,559,953	1,167,899	1,034,254
Expenditures for long-lived assets	284,109	166,331	247,895
Depreciation and amortization	74,088	66,807	63,447
Operating Segments | Aftermarket Segment
Segment Reporting Information
Net sales	628,255	279,581	233,191
Operating profit (loss)	66,842	34,920	31,329
Total assets	615,425	595,688	129,776
Expenditures for long-lived assets	15,150	302,857	20,544
Depreciation and amortization	$ 23,892	$ 8,551	$ 4,079