Segment Reporting (Schedule of Information Relating to Segments) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information
Net sales to external customers	$ 402,899	$ 412,370	$ 440,831	$ 422,798	$ 334,228	$ 345,296	$ 362,085	$ 361,457	$ 1,678,898	$ 1,403,066	$ 1,190,782
Operating profit (loss)									200,850	116,254	95,487
Total assets	786,904				622,856				786,904	622,856	543,841
Expenditures for long-lived assets									86,602	67,587	147,370
Depreciation and amortization									46,167	41,624	32,596
Purchase of long-lived assets as part of business acquisition									42,000	38,600	105,000
OEM Segment
Segment Reporting Information
Net sales to external customers									1,548,091	1,300,060	1,127,026
Aftermarket Segment
Segment Reporting Information
Net sales to external customers									130,807	103,006	63,756
Corporate and Other
Segment Reporting Information
Operating profit (loss)									0	(3,716)	(1,954)
Total assets	152,308				65,439				152,308	65,439	48,225
Depreciation and amortization									$ 276	$ 143	$ 88
Net sales | OEM Segment
Segment Reporting Information
Consolidated risk, percentage									92.00%	93.00%	95.00%
Net sales | Aftermarket Segment
Segment Reporting Information
Consolidated risk, percentage									8.00%	7.00%	5.00%
Customer Concentration Risk | Net sales | Thor Industries, Inc.
Segment Reporting Information
Consolidated risk, percentage									37.00%	28.00%	33.00%
Customer Concentration Risk | Net sales | Berkshire Hathaway Inc.
Segment Reporting Information
Consolidated risk, percentage									26.00%	26.00%	28.00%
Customer Concentration Risk | Net sales | Jayco, Inc.
Segment Reporting Information
Consolidated risk, percentage										10.00%
International | Geographic Concentration Risk | Net sales
Segment Reporting Information
Consolidated risk, percentage									2.00%	1.00%	1.00%
Operating Segments
Segment Reporting Information
Net sales to external customers									$ 1,678,898	$ 1,403,066	$ 1,190,782
Operating profit (loss)									200,850	119,970	97,441
Total assets	634,596				557,417				634,596	557,417	495,616
Expenditures for long-lived assets									86,602	67,587	147,370
Depreciation and amortization									45,891	41,481	32,508
Operating Segments | OEM Segment
Segment Reporting Information
Net sales to external customers									1,548,091	1,300,060	1,127,026
Operating profit (loss)									180,850	105,224	88,744
Total assets	569,385				500,734				569,385	500,734	441,127
Expenditures for long-lived assets									80,588	65,492	119,715
Depreciation and amortization									42,593	38,583	30,954
Operating Segments | Aftermarket Segment
Segment Reporting Information
Net sales to external customers									130,807	103,006	63,756
Operating profit (loss)									20,000	14,746	8,697
Total assets	$ 65,211				$ 56,683				65,211	56,683	54,489
Expenditures for long-lived assets									6,014	2,095	27,655
Depreciation and amortization									$ 3,298	$ 2,898	$ 1,554