Segment Reporting (Schedule of Automotive and Other Segment Reporting) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 459,570,000	$ 438,628,000	$ 443,139,000	$ 453,535,000	$ 419,913,000	$ 429,643,000	$ 423,801,000	$ 405,568,000	$ 1,794,872,578	$ 1,678,924,756	$ 1,543,617,706
Income (Loss) from Operations	133,994,000	$ 129,073,000	$ 125,865,000	$ 134,427,000	127,936,000	$ 134,212,000	$ 128,746,000	$ 120,849,000	523,358,352	511,742,935	458,766,439
Assets	2,352,053,912				2,309,619,833				2,352,053,912	2,309,619,833	2,148,672,928
Depreciation & Amortization									99,570,908	88,587,430	80,599,167
Capital Expenditures									104,040,919	120,955,614	97,941,762
Corporate
Segment Reporting Information [Line Items]
Assets	870,415,748				842,246,344				870,415,748	842,246,344	724,816,255
Depreciation & Amortization									3,891,873	1,729,886	1,366,927
Capital Expenditures									21,166,986	20,944,269	147,996
Automotive Products
Segment Reporting Information [Line Items]
Revenues									1,758,127,468	1,639,692,243	1,506,872,004
Income (Loss) from Operations									512,895,699	497,753,966	445,067,511
Automotive Products | Operating Segments
Segment Reporting Information [Line Items]
Assets	1,472,061,650				1,457,989,335				1,472,061,650	1,457,989,335	1,414,426,679
Depreciation & Amortization									95,378,100	86,567,248	78,925,332
Capital Expenditures									82,703,576	99,811,083	97,632,519
Other
Segment Reporting Information [Line Items]
Revenues									36,745,110	39,232,514	36,745,702
Income (Loss) from Operations									10,462,653	13,988,969	13,698,928
Other | Operating Segments
Segment Reporting Information [Line Items]
Assets	$ 9,576,514				$ 9,384,154				9,576,514	9,384,154	9,429,994
Depreciation & Amortization									300,935	290,296	306,908
Capital Expenditures									170,357	200,262	161,247
United States | Automotive Products
Segment Reporting Information [Line Items]
Revenues									567,492,812	554,945,912	494,876,354
Germany | Automotive Products
Segment Reporting Information [Line Items]
Revenues									351,123,204	328,208,190	295,044,988
Japan | Automotive Products
Segment Reporting Information [Line Items]
Revenues									185,261,067	154,005,299	148,632,237
Other | Automotive Products
Segment Reporting Information [Line Items]
Revenues									$ 654,250,385	$ 602,532,841	$ 568,318,425