Gentex (GNTX) 10-K 21 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 01, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Entity Registrant Name	GENTEX CORP
Entity Central Index Key	355,811
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		274,421,032
Entity Public Float			$ 5,284,326,964
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($)	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Cash and cash equivalents	$ 569,734,496	$ 546,477,075
Short-term investments	152,538,054	177,021,197
Accounts receivable, net	231,121,788	211,591,745
Inventories, net	216,765,583	189,311,437
Prepaid expenses and other	14,403,902	30,587,575
Total current assets	1,184,563,823	1,154,989,029
PLANT AND EQUIPMENT:
Land, buildings and improvements	317,600,833	294,696,813
Machinery and equipment	790,833,278	721,713,250
Construction-in-process	35,828,403	30,643,709
Total Plant and Equipment	1,144,262,514	1,047,053,772
Less- Accumulated depreciation	(651,783,184)	(581,231,305)
Net Plant and Equipment	492,479,330	465,822,467
OTHER ASSETS:
Goodwill	307,365,845	307,365,845
Long-term investments	57,782,418	49,894,363
Intangible Assets, net	288,975,000	308,275,000
Patents and other assets, net	20,887,496	23,273,129
Total Other Assets	675,010,759	688,808,337
TOTAL ASSETS	2,352,053,912	2,309,619,833
CURRENT LIABILITIES:
Accounts payable	89,898,467	79,963,630
Accrued liabilities:
Salaries, wages and vacation	18,502,209	12,378,007
Income Taxes	360,014	572,834
Royalties	14,660,864	11,932,416
Dividends payable	28,028,132	25,896,376
Current portion of long term debt	78,000,000	7,500,000
Other	14,197,321	11,614,716
Total current liabilities	243,647,007	149,857,979
LONG TERM DEBT	0	178,125,000
DEFERRED INCOME TAXES	58,888,644	71,212,620
TOTAL LIABILITIES	302,535,651	399,195,599
SHAREHOLDERS’ INVESTMENT:
Preferred stock, no par value, 5,000,000 shares authorized; none issued or outstanding	0	0
Common stock, par value $.06 per share; 400,000,000 shares authorized; 280,281,321 and 287,737,516 shares issued and outstanding in 2017 and 2016 respectively.	16,816,879	17,264,251
Additional paid-in capital	723,510,672	683,446,463
Retained earnings	1,301,997,327	1,210,984,825
Accumulated other comprehensive income:
Unrealized gain on investments	6,626,379	2,788,975
Unrealized gain (loss) on derivatives	(78,026)	(1,197,281)
Cumulative translation adjustment	645,030	(2,862,999)
Total shareholders’ investment	2,049,518,261	1,910,424,234
TOTAL LIABILITES AND SHAREHOLDERS' INVESTMENT	$ 2,352,053,912	$ 2,309,619,833

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.06	$ 0.06
Common stock, shares authorized (in shares)	400,000,000	400,000,000
Common stock, shares issued (in shares)	280,281,321	287,737,516
Common stock, shares outstanding (in shares)	280,281,321	287,737,516

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
NET SALES	$ 1,794,872,578	$ 1,678,924,756	$ 1,543,617,706
COST OF GOODS SOLD	1,100,344,312	1,010,472,512	939,841,654
Gross profit	694,528,266	668,452,244	603,776,052
OPERATING EXPENSES:
Engineering, research and development	99,726,438	94,238,032	88,392,919
Selling, general and administrative	71,443,476	62,471,277	56,616,694
Total operating expenses	171,169,914	156,709,309	145,009,613
Income from operations	523,358,352	511,742,935	458,766,439
OTHER INCOME:
Investment income	9,442,387	4,787,128	4,990,811
Other, net	(1,004,035)	(5,969,290)	(165,794)
Total other income (expense)	8,438,352	(1,182,162)	4,825,017
Income before provision for income taxes	531,796,704	510,560,773	463,591,456
PROVISION FOR INCOME TAXES	125,004,782	162,969,497	145,121,597
NET INCOME	$ 406,791,922	$ 347,591,276	$ 318,469,859
EARNINGS PER SHARE:
Basic (in dollars per share)	$ 1.42	$ 1.21	$ 1.09
Diluted (in dollars per share)	1.41	1.19	1.08
Cash Dividends Declared per Share (in dollars per share)	$ 0.39	$ 0.355	$ 0.335

Consolidated Statement of Compr

Consolidated Statement of Comprehensive Income - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net Income	$ 406,791,922	$ 347,591,276	$ 318,469,859
Other comprehensive income (loss) before tax:
Foreign currency translation adjustments	3,508,029	(2,818,090)	(1,448,808)
Unrealized gains (losses) on derivatives	1,721,933	1,105,468	(1,471,736)
Unrealized gains (losses) on available-for-sale securities, net	5,903,699	3,013,951	(15,443,716)
Other comprehensive income (loss), before tax	11,133,661	1,301,328	(18,364,260)
Expense (Benefit) for income taxes related to components of other comprehensive income (loss)	2,668,973	1,441,798	(5,920,409)
Other comprehensive income (loss), net of tax	8,464,688	(140,469)	(12,443,851)
Comprehensive Income	$ 415,256,610	$ 347,450,807	$ 306,026,008

Consolidated Statement of Share

Consolidated Statement of Shareholders' Investment - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		287,737,516			287,737,516
Beginning balance		$ 1,910,424,234		$ 1,722,516,761	$ 1,910,424,234	$ 1,722,516,761	$ 1,571,412,445
Issuance of common stock and the tax benefit of stock plan transactions					47,770,467	86,893,439	33,006,225
Repurchases of common stock					(231,363,216)	(163,361,221)	(111,228,825)
Stock-based compensation expense related to stock options, employee stock purchases and restricted stock					18,376,965	19,192,699	21,430,991
Dividends declared					(110,946,799)	(102,268,251)	(98,130,083)
Net Income	$ 130,469,000	$ 97,557,000	$ 88,761,000	$ 80,280,000	406,791,922	347,591,276	318,469,859
Other comprehensive income					$ 8,464,688	$ (140,469)	(12,443,851)
Ending balance (in shares)	280,281,321		287,737,516		280,281,321	287,737,516
Ending balance	$ 2,049,518,261		$ 1,910,424,234		$ 2,049,518,261	$ 1,910,424,234	$ 1,722,516,761
Common Stocks
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		287,737,516		291,338,011	287,737,516	291,338,011	295,247,958
Beginning balance		$ 17,264,251		$ 17,480,281	$ 17,264,251	$ 17,480,281	$ 17,714,877
Issuance of common stock and the tax benefit of stock plan transactions (in shares)					4,498,729	6,705,632	2,740,626
Issuance of common stock and the tax benefit of stock plan transactions					$ 269,923	$ 402,338	$ 164,438
Repurchases of common stock (in shares)					(11,954,924)	(10,306,127)	(6,650,573)
Repurchases of common stock					$ (717,295)	$ (618,368)	$ (399,034)
Ending balance (in shares)	280,281,321		287,737,516		280,281,321	287,737,516	291,338,011
Ending balance	$ 16,816,879		$ 17,264,251		$ 16,816,879	$ 17,264,251	$ 17,480,281
Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		683,446,463		596,782,695	683,446,463	596,782,695	553,836,483
Issuance of common stock and the tax benefit of stock plan transactions					47,500,544	86,491,101	32,841,787
Repurchases of common stock					(25,813,300)	(19,020,032)	(11,326,566)
Stock-based compensation expense related to stock options, employee stock purchases and restricted stock					18,376,965	19,192,699	21,430,991
Ending balance	723,510,672		683,446,463		723,510,672	683,446,463	596,782,695
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		1,210,984,825		1,109,384,621	1,210,984,825	1,109,384,621	988,548,070
Repurchases of common stock					(204,832,621)	(143,722,821)	(99,503,225)
Dividends declared					(110,946,799)	(102,268,251)	(98,130,083)
Net Income					406,791,922	347,591,276	318,469,859
Ending balance	1,301,997,327		1,210,984,825		1,301,997,327	1,210,984,825	1,109,384,621
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		$ (1,271,305)		$ (1,130,836)	(1,271,305)	(1,130,836)	11,313,015
Other comprehensive income					8,464,688	(140,469)	(12,443,851)
Ending balance	$ 7,193,383		$ (1,271,305)		$ 7,193,383	$ (1,271,305)	$ (1,130,836)

Consolidated Statement of Shar7

Consolidated Statement of Shareholders' Investment (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Dividends declared per share (in dollars per share)	$ 0.39	$ 0.355	$ 0.335

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net Income	$ 406,791,922	$ 347,591,276	$ 318,469,859
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	99,570,908	88,587,430	80,599,167
Gain on disposal of assets	(188,150)	(146,261)	(10,900)
Loss on disposal of assets	299,174	1,080,486	455,950
Gain on sale of investments	(1,309,166)	(4,239,895)	(9,666,482)
Loss on sale of investments	375,388	3,919,698	2,705,601
Deferred income taxes	(14,996,179)	22,498,361	13,058,458
Stock based compensation expense related to employee stock options, employee stock purchases and restricted stock	18,376,965	19,192,699	21,430,991
Change in operating assets and liabilities:
Accounts receivable	(19,530,043)	(15,622,345)	(27,960,696)
Inventories	(27,454,146)	(14,616,026)	(32,937,525)
Prepaid expenses and other	16,183,673	4,399,366	(9,530,002)
Accounts payable	9,934,837	13,609,856	(5,103,209)
Accrued liabilities	12,947,597	10,793,540	2,904,940
Net cash flows from operating activities	501,002,780	477,048,185	354,416,152
Activity in available-for-sale securities:
Sales proceeds	30,207,523	87,293,155	58,517,164
Maturities and calls	23,100,000	5,500,000	0
Purchases	(29,874,960)	(216,670,674)	(47,513,972)
Plant and equipment additions	(104,040,919)	(120,955,614)	(97,941,762)
Proceeds from sale of plant and equipment	249,757	665,191	43,544
Increase in other assets	2,646,029	(7,278,166)	(2,842,635)
Net cash used for investing activities	(77,712,570)	(251,446,108)	(89,737,661)
CASH FLOWS USED FOR FINANCING ACTIVITIES:
Repayment of long-term debt	(107,625,000)	(47,500,000)	(32,500,000)
Issuance of common stock from stock plan transactions	47,770,467	81,310,048	30,168,496
Cash dividends paid	(108,815,040)	(101,131,356)	(96,990,439)
Repurchases of common stock	(231,363,216)	(163,361,221)	(111,228,825)
Net cash used for financing activities	(400,032,789)	(230,682,529)	(210,550,768)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	23,257,421	(5,080,452)	54,127,723
CASH AND CASH EQUIVALENTS, Beginning of year	546,477,075	551,557,527	497,429,804
CASH AND CASH EQUIVALENTS, End of year	$ 569,734,496	$ 546,477,075	$ 551,557,527

Summary of Significant Accounti

Summary of Significant Accounting and Reporting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary Of Significant Accounting And Reporting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING AND REPORTING POLICIES The Company Gentex Corporation designs and manufactures automatic-dimming rearview mirrors and electronics for the automotive industry, dimmable aircraft windows for the aviation industry, and commercial smoke alarms and signaling devices for the fire protection industry. The Company’s largest business segment involves designing, developing, manufacturing and marketing interior and exterior automatic-dimming automotive rearview mirrors and various electronic modules. The Company ships its product to all of the major automotive producing regions worldwide, which it supports with numerous sales, engineering and distribution locations worldwide. A substantial portion of the Company’s net sales and accounts receivable result from transactions with domestic and foreign automotive manufacturers and Tier 1 suppliers. Aircraft windows are sold for use by aircraft manufacturers and a Tier 1 supplier. The Company’s fire protection products are primarily sold to domestic distributors and original equipment manufacturers of fire and security systems. The Company does not require collateral or other security for trade accounts receivable. Significant accounting policies of the Company not described elsewhere are as follows: Consolidation The consolidated financial statements include the accounts of Gentex Corporation and all of its wholly-owned subsidiaries (together the “Company”). All significant intercompany accounts and transactions have been eliminated. Cash Equivalents Cash equivalents consist of funds invested in bank accounts and money market funds that have daily liquidity. Allowance For Doubtful Accounts The Company bases its allowances for doubtful accounts related to receivables on historical credit and collections experience, and the specific identification of other potential problems impacting collectability, including the economic climate. Actual collections can differ, requiring adjustments to the allowances. Individual accounts receivable balances are evaluated on a monthly basis, and those balances considered uncollectible are charged to the allowance. Collections of amounts previously written off are recorded as an increase to the allowance. The following table presents the activity in the Company’s allowance for doubtful accounts: Beginning Balance Net Additions/ (Reductions) to Costs and Expenses Deductions and Other Adjustments Ending Balance Year Ended December 31, 2017: Allowance for Doubtful Accounts $ 2,917,424 $ — $ (202,891 ) $ 2,714,533 Year Ended December 31, 2016: Allowance for Doubtful Accounts $ 2,663,477 $ — $ 253,947 $ 2,917,424 Year Ended December 31, 2015: Allowance for Doubtful Accounts $ 2,711,248 $ — $ (47,771 ) $ 2,663,477 The Company’s overall allowance for doubtful accounts primarily relates to financially distressed automotive customers. The Company continues to work with these financially distressed customers in collecting past due balances. Investments The Company follows the provisions of ASC 820, Fair Value Measurements and Disclosures, for its financial assets and liabilities, and for its non-financial assets and liabilities subject to fair value measurements. ASC 820 provides a framework for measuring the fair value of assets and liabilities. This framework is intended to provide increased consistency in how fair value determinations are made under various existing accounting standards that permit, or in some cases, require estimates of fair-market value. This standard also expanded financial statement disclosure requirements about a company’s use of fair-value measurements, including the effect of such measure on earnings. The cost of securities sold is based on the specific identification method. The Company’s common stocks and certain mutual funds are classified as available for sale and are stated at fair value based on quoted market prices, and as such are classified as Level 1 assets. The Company determines the fair value of its government securities, corporate bonds, and certain mutual funds by utilizing monthly valuation statements that are provided by its broker. The broker determines the investment valuation by utilizing the bid price in the market and also refers to third party sources to validate valuations, and as such are classified as Level 2 assets. The Company's certificates of deposit have remaining maturities of less than one year and are classified as available for sale, and are considered as Level 1 assets. These investments are carried at cost, which approximates fair value. Assets or liabilities that have recurring fair value measurements are shown below as of December 31, 2017 and December 31, 2016 : Fair Value Measurements at Reporting Date Using Total as of Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Description December 31, 2017 (Level I) (Level 2) (Level 3) Cash & Cash Equivalents $ 569,734,496 $ 569,734,496 $ — $ — Short-Term Investments: Certificate of Deposit 130,000,000 130,000,000 — — Government Securities 9,011,130 — 9,011,130 — Mutual Funds 393,581 — 393,581 — Corporate Bonds 12,944,999 — 12,944,999 — Other 188,344 188,344 — — Long-Term Investments: Corporate Bonds 3,018,720 — 3,018,720 — Common Stocks 15,703,371 15,703,371 — — Mutual Funds 34,681,337 34,681,337 — — Preferred Stock 1,178,991 1,178,991 — — Total $ 776,854,969 $ 751,486,539 $ 25,368,430 $ — Fair Value Measurements at Reporting Date Using Total as of Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Description December 31, 2016 (Level I) (Level 2) (Level 3) Cash & Cash Equivalents $ 546,477,075 $ 546,477,075 $ — $ — Short-Term Investments: Certificate of Deposit 130,000,000 130,000,000 — — Government Securities 13,993,480 — 13,993,480 — Mutual Funds 26,116,681 — 26,116,681 — Corporate Bonds 6,698,382 — 6,698,382 — Other 212,653 212,653 — — Long-Term Investments: Corporate Bonds 1,948,556 — 1,948,556 — Common Stocks 12,849,007 12,849,007 — — Mutual Funds 28,872,010 28,872,010 — — Preferred Stock 714,000 714,000 — — Government Securities 5,510,790 — 5,510,790 — Total $ 773,392,634 $ 719,124,745 $ 54,267,889 $ — The amortized cost, unrealized gains and losses, and market value of investment securities are shown as of December 31, 2017 and 2016 : Unrealized 2017 Cost Gains Losses Market Value Short-Term Investments: Certificate of Deposit $ 130,000,000 $ — $ — $ 130,000,000 Government Securities 9,024,777 — (13,647 ) 9,011,130 Mutual Funds 392,482 1,575 (476 ) 393,581 Corporate Bonds 12,952,229 — (7,230 ) 12,944,999 Other 188,344 — — 188,344 Long-Term Investments: Corporate Bonds 3,022,994 — (4,274 ) 3,018,720 Common Stocks 10,897,219 5,079,815 (273,663 ) 15,703,371 Mutual Funds 29,306,540 5,440,344 (65,547 ) 34,681,337 Preferred Stock 1,141,458 40,533 (3,000 ) 1,178,991 Total $ 196,926,043 $ 10,562,267 $ (367,837 ) $ 207,120,473 Unrealized 2016 Cost Gains Losses Market Value Short-Term Investments: Certificate of Deposit $ 130,000,000 $ — $ — $ 130,000,000 Government Securities 14,003,644 — (10,164 ) 13,993,480 Mutual Funds 26,326,674 27,459 (237,452 ) 26,116,681 Corporate Bonds 6,706,721 — (8,339 ) 6,698,382 Other 212,653 — — 212,653 Long-Term Investments: Corporate Bonds 1,955,292 — (6,736 ) 1,948,556 Common Stocks 9,825,550 3,349,962 (326,505 ) 12,849,007 Mutual Funds 27,329,164 1,830,992 (288,146 ) 28,872,010 Preferred Stock 745,462 360 (31,822 ) 714,000 Government Securities 5,519,668 661 (9,539 ) 5,510,790 Total $ 222,624,828 $ 5,209,434 $ (918,703 ) $ 226,915,559 Unrealized losses on investments as of December 31, 2017 are as follows: Aggregate Unrealized Losses Aggregate Fair Value Less than one year $ 263,655 $ 31,223,557 Greater than one year 104,182 285,077 Total $ 367,837 $ 31,508,634 Unrealized losses on investments as of December 31, 2016 are as follows: Aggregate Unrealized Losses Aggregate Fair Value Less than one year $ 767,612 $ 55,574,292 Greater than one year 151,091 358,120 Total $ 918,703 $ 55,932,412 ASC 320, Accounting for Certain Investments in Debt and Equity Securities , as amended and interpreted, provides guidance on determining when an investment is other-than-temporarily impaired. The Company reviews its fixed income and equity investment portfolio for any unrealized losses that would be deemed other-than-temporary and require the recognition of an impairment loss in income. If the cost of an investment exceeds its fair value, the Company evaluates, among other factors, general market conditions, the duration and extent to which the fair value is less than cost, and the Company’s intent and ability to hold the investments. Management also considers the type of security, related-industry and sector performance, as well as published investment ratings and analyst reports, to evaluate its portfolio. Once a decline in fair value is determined to be other-than-temporary, an impairment charge is recorded and new cost basis in the investment is established. If market, industry, and/or investee conditions deteriorate, the Company may incur future impairments. No investments were considered to be other-than-temporary impaired in 2017 and 2016 . Fixed income securities as of December 31, 2017 , have contractual maturities as follows: Due within one year $ 151,956,129 Due between one and five years 4,197,711 Due over five years — $ 156,153,840 Fair Value of Financial Instruments The Company’s financial instruments consist of cash and cash equivalents, investments, accounts receivable accounts payable, short and long term debt. The Company’s estimate of the fair values of these financial instruments approximates their carrying amounts at December 31, 2017 and 2016 . Inventories Inventories include material, direct labor and manufacturing overhead and are valued at the lower of first-in, first-out (FIFO) cost or market. Inventories consisted of the following as of December 31, 2017 and 2016 : 2017 2016 Raw materials $ 139,272,129 $ 115,099,569 Work-in-process 30,481,192 32,509,368 Finished goods 47,012,262 41,702,500 Total Inventory $ 216,765,583 $ 189,311,437 Allowances for slow-moving and obsolete inventories (which are included, net, in the above inventory values) were $6.6 million and $6.1 million at December 31, 2017 and 2016 . The overall allowance remained consistent at 3% of the inventory balance. Plant and Equipment Plant and equipment is stated at cost. Depreciation and amortization are computed for financial reporting purposes using the straight-line method, with estimated useful lives of 7 to 30 years for buildings and improvements, and 3 to 10 years for machinery and equipment. Depreciation expense was approximately $77.0 million , $66.3 million and $58.1 million in 2017 , 2016 and 2015 , respectively. Impairment or Disposal of Long-Lived Assets The Company reviews long-lived assets, including property, plant and equipment and other intangible assets with definite lives, for impairment whenever events or changes in circumstances indicate that the asset’s carrying amount may not be recoverable. The Company conducts its long-lived asset impairment analysis in accordance with ASC 360-10-15, Impairment or Disposal of Long-Lived Assets . ASC 360-10-15 requires the Company to group assets and liabilities at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities and evaluate the asset group against the sum of the undiscounted future cash flows. If the undiscounted cash flows do not indicate the carrying amount of the asset is recoverable, an impairment charge is measured as the amount by which the carrying amount of the asset group exceeds its fair value based on discounted cash flow analysis or appraisals. Patents The Company’s policy is to capitalize costs incurred to obtain patents. The cost of patents is amortized over their useful lives. The cost of patents in process is not amortized until issuance. The Company periodically obtains intellectual property rights, in the ordinary course of business, and the cost of the rights are amortized over their useful lives. Goodwill and Intangible Assets Goodwill reflects the cost of an acquisition in excess of the fair values assigned to identifiable net assets acquired. The Company reviews goodwill for impairment during the fourth quarter on an annual basis or more frequently if events or changes in circumstances indicate that goodwill might be impaired. The Company performs an impairment review for its automotive reporting unit, which has been determined to be one of the Company’s reportable segments using a fair value method which incorporates management’s judgments and assumptions, as well as incorporates third party valuations. The fair value of a reporting unit refers to the price that would be received to sell the unit as a whole in an orderly transaction between market participants at the measurement date. In estimating the fair value, the Company uses a combination of widely accepted valuation methodologies incorporating certain judgments and assumptions to arrive at the fair value of the reporting unit. The assumptions included in the impairment tests require judgment and changes to these inputs could impact the results of the calculations which could result in an impairment charge in future periods if the carrying amount of the reporting unit exceeds its calculated fair value. Other than management's internal projections of future cash flows, the primary assumptions used in the step 1 and step 2 impairment tests are the weighted-average cost of capital and long-term growth rates. Although the Company's cash flow forecasts are based on assumptions that are considered reasonable by management and consistent with the plans and estimates management is using to operate the underlying business, there are significant judgments in determining the expected future cash flows attributable to a reporting unit. There have been no impairment charges booked currently or in prior periods in which goodwill existed. Indefinite lived intangible assets are also subject to annual impairment testing or more frequently if indicators of impairment are identified. Management judgment and assumptions are required in determining the underlying fair value of the indefinite lived intangible assets. While the Company believes the judgments and assumptions used in determining fair value are reasonable, different assumptions could change the estimated fair values and, therefore, impairment charges could be required, which could be material to the consolidated financial statements. The indefinite lived intangible assets were not impaired as a result of the annual test prepared by management for either period presented. Revenue Recognition The Company’s revenue is generated from sales of its products. Sales are recognized when the product is shipped and legal title has passed to the customer. The Company does not generate sales from arrangements with multiple deliverables. Effective January 1, 2018, the Company adopted ASC Topic 606, Revenue from Contracts with Customers , using the modified retrospective method. This guidance supersedes nearly all existing revenue recognition guidance under US GAAP. The core principle of the guidance is that an entity should recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The Company has drafted its accounting policy for the new standard based on a detailed review of its business and contracts. Based on the new guidance, the Company expects to continue recognizing revenue at a particular point in time for the majority of its contracts with customers, which is generally when products are either shipped or delivered, and therefore the adoption of the standard did not have a material impact on its consolidated financial statements. Advertising and Promotional Materials All advertising and promotional costs are expensed as incurred and amounted to approximately $2.6 million , $1.9 million and $1.4 million , in 2017 , 2016 and 2015 , respectively. Repairs and Maintenance Major renewals and improvements of property and equipment are capitalized, and repairs and maintenance are expensed as incurred. The Company incurred expenses relating to the repair and maintenance of plant and equipment of approximately $24.6 million , $22.1 million and $20.7 million , in 2017 , 2016 and 2015 , respectively. Self-Insurance The Company is self-insured for a portion of its risk on workers’ compensation and employee medical costs. The arrangements provide for stop loss insurance to manage the Company’s risk. Operations are charged with the cost of claims reported and an estimate of claims incurred but not reported, based upon historical claims lag information and other data. Product Warranty The Company periodically incurs product warranty costs. Any liabilities associated with product warranty are estimated based on known facts and circumstances and are not significant at December 31, 2017 , 2016 and 2015 . The Company does not offer extended warranties on its products. Income Taxes The provision for income taxes is based on the earnings reported in the consolidated financial statements. Deferred income tax assets and liabilities are computed for differences between the financial statement and tax basis of assets and liabilities that will result in taxable or deductible amounts in the future. Such deferred income tax asset and liability computations are based on enacted tax laws and rates. Earnings Per Share The following table reconciles the numerators and denominators used in the calculations of basic and diluted earnings per share (EPS) for each of the last three years: 2017 2016 2015 Numerators: Numerator for both basic and diluted EPS, net income $ 406,791,922 $ 347,591,276 $ 318,469,859 Denominators: Denominator for basic EPS, weighted-average common shares outstanding 285,864,997 288,433,772 293,096,212 Potentially dilutive shares resulting from stock option plans 2,361,092 2,638,544 3,141,687 Denominator for diluted EPS 288,226,089 291,072,316 296,237,899 For the years ended December 31, 2017 , 2016 and 2015 , 910,105 shares, 1,985,849 shares, and 1,656,936 shares, respectively, related to stock option plans were not included in diluted average common shares outstanding because they were anti-dilutive. Other Comprehensive Income (Loss) Comprehensive income (loss) reflects the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. For the Company, comprehensive income represents net income adjusted for unrealized gains and losses on certain investments, unrealized gains and losses on certain derivative financial instruments, and foreign currency translation adjustments that are further detailed in Note 9 to the Consolidated Financial Statements. Foreign Currency Translation The financial position and results of operations of the Company’s foreign subsidiaries are measured using the local currency as the functional currency. Assets and liabilities are translated at the exchange rate in effect at year-end. Income statement accounts are translated at the average rate of exchange in effect during the year. The resulting translation adjustment is recorded as a separate component of shareholders’ investment. Gains and losses arising from re-measuring foreign currency transactions into the appropriate currency are included in the determination of net income. Derivative Financial Instruments The Company accounts for derivative financial instruments in accordance with the guidance provided in ASC Topic 815, Derivatives and Hedging. The guidance requires that all derivative instruments be recognized as assets or liabilities on the consolidated balance sheets and measured at fair value. For derivatives designated as cash flow hedges, fair value changes in the effective portion of the hedging instrument are recognized in accumulated other comprehensive income on the consolidated balance sheets until the forecasted transaction affects earnings of the consolidated entity. Any ineffective portion of the fair value change is recognized in earnings immediately. The Company reported a loss of $.1 million in earnings for the year ended December 31, 2017 as a result of the ineffectiveness of the hedge. As of December 31, 2016, there was no ineffectiveness. The Company seeks to reduce exposure to interest rate fluctuations through the use of an interest rate swap agreement. The Company does not buy and sell such financial instruments for investment or speculative purposes. The Company is exposed to credit loss in the event of nonperformance by the counterparties on derivative contracts. It is the Company’s practice to manage its credit risk on these transactions by dealing with highly rated financial institutions. Stock-Based Compensation Plans The Company accounts for stock-based compensation using the fair value recognition provisions of ASC 718, “Compensation - Stock Compensation.” As described more fully in Note 5, the Company provides compensation benefits under two stock option plans, a restricted stock plan and an employee stock purchase plan. Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Recent Accounting Standards In March 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-09, Improvements to Employee Share-Based Payment Accounting , which amends Accounting Standards Codification (ASC) Topic 718, Compensation - Stock Compensation . ASU 2016-09 simplifies several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. Under previous guidance, excess tax benefits and deficiencies from stock-based compensation arrangements were recorded in equity when the awards vested or were settled. ASU 2016-09 requires prospective recognition of excess tax benefits and deficiencies in the income statement as a component of the income tax provision. In addition, under ASU 2016-09, excess income tax benefits from stock-based compensation arrangements are classified as cash flow from operations, rather than as cash flow from financing activities. ASU 2016-09 also allows for the Company to make an entity-wide accounting policy election to either estimate the number of awards that are expected to vest or account for forfeitures when they occur. The Company will continue to apply its existing entity-wide policy to estimate the number of awards expected to be forfeited. The Company adopted this standard in the first quarter of 2017. Impact to Consolidated Statements of Income One of the more significant impacts of adopting ASU 2016-09 is the required change in how the Company recognizes the excess tax benefits or deficiencies related to share-based compensation. For example, prior to adopting ASU 2016-09 such benefits and deficiencies were credited or charged, respectively, to additional paid-in capital in the Company’s Consolidated Balance Sheets. Under ASU 2016-09, these benefits and deficiencies are recognized as a discrete tax benefit or discrete tax expense, in the Company’s Consolidated Statements of Income. For the years ended December 31, 2017, the Company recognized a net discrete tax benefit of $5.2 million , related to net tax benefits from share-based compensation. ASU 2016-09 requires companies to adopt the amendment related to accounting for benefits and deficiencies on a prospective basis only. As a result, no change has been made to the Consolidated Statements of Income for the years ended December 31, 2016 and 2015 related to the $3.2 million and $1.2 million of net tax benefits the Company recognized as additional paid-in capital during each respective period. Net tax benefits of $3.2 million recognized as additional paid-in-capital during the year ended December 31, 2016 includes gross tax benefits of $4.9 million net of $1.7 million tax expense. Net tax benefits of $1.2 million recognized as additional paid-in-capital during the year ended December 31, 2015 includes gross tax benefits of $1.7 million net of $.5 million tax expense. In consideration of the impact of the adoption of this standard to earnings per share, the total impact of adoption of this standard to the earnings per share calculation was less than $.02 for the year ending December 31, 2017. Impact to Consolidated Statements of Cash Flows In addition to the income tax consequences described above, under ASU 2016-09 all tax benefits related to share-based payments are reported as cash flows from operating activities along with all other income tax cash flows. Previously, tax benefits from share-based payment arrangements were reported as cash flows from financing activities. With respect to the classification of tax benefits on the statement of cash flows, ASU 2016-09 allows companies to elect either a prospective or retrospective application. The Company has elected to apply this classification amendment retrospectively. As a result, the Company elected to reclassify $5.6 million of tax expense previously reported as cash flows from financing activities on the Company’s Consolidated Statement of Cash Flows for the twelve months ended December 31, 2016 as cash flows from operating activities. Effective January 1, 2018, the Company adopted ASC Topic 606, Revenue from Contracts with Customers , using the modified retrospective method. This guidance supersedes nearly all existing revenue recognition guidance under US GAAP. The core principle of the guidance is that an entity should recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The Company has drafted its accounting policy for the new standard based on a detailed review of its business and contracts. Based on the new guidance, the Company continues to recognize revenue at a particular point in time for the majority of its contracts with customers, which is generally when products are either shipped or delivered. Therefore, the adoption of ASC 606 did not have a material impact on the consolidated financial statements. The Company anticipates it will expand its consolidated financial statement disclosures in order to comply with the disclosure requirements of the ASU beginning in the first quarter of 2018. Effective January 1, 2018, the Company adopted ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilitie s. The standard amends various aspects of the recognition, measurement, presentation, and disclosure of financial instruments. The most significant impact to our consolidated financial statements relates to the recognition and measurement of equity investments at fair value with changes recognized in Net income. The amendment also updates certain presentation and disclosure requirements. The Company will have a cumulative-effect adjustment in the first quarter of 2018 of approximately $7 million as a result of the implementation of this guidance, as a result of the reclassification of the net unrealized gain for available-for-sale securities as of December 31, 2017 from other comprehensive income to retained earnings. The adoption of ASU 2016-01 is expected to increase volatility in net income as changes in the fair value of available-for-sale equity investments and changes in observable prices of equity investments without readily determinable fair values will be recorded in net income. In February 2016, the FASB issued ASU 2016-02, Leases , which provides guidance for lease accounting. The new guidance contained in the ASU stipulates that lessees will need to recognize a right-of-use asset and a lease liability for substantially all leases (other than leases that meet the definition of a short-term lease). The liability will be equal to the present value of lease payments. Treatment in the consolidated statements of earnings will be similar to the current treatment of operating and capital leases. The new guidance is effective on a modified retrospective basis for the Company in the first quarter of its fiscal year ending December 31, 2019. The Company is currently in the process of evaluating the impact of adoption of this standard on its consolidated financial statements.

Debt and Financing Arrangements

Debt and Financing Arrangements	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Debt and Financing Arrangements	DEBT AND FINANCING ARRANGEMENTS On September 27, 2013, the Company entered into a Credit Agreement (the “Credit Agreement”) with certain banks and agents. Pursuant to the Credit Agreement, the Company is borrower under a $150 million senior revolving credit facility ("Revolver") and a $150 million term loan facility ("Term Loan"). Under the terms of the Credit Agreement, the Company is entitled to further request an additional aggregate principal amount of up to $75 million , subject to the satisfaction of certain conditions. In addition, the Company is entitled to the benefit of swing loans from amounts otherwise available under the Revolver in the aggregate principal amount of up to $20 million and to request Letters of Credit from amounts otherwise available under the Revolver in the aggregate principal amount of up to $20 million , both subject to certain conditions. The obligations of the Company under the Credit agreement are not secured, but are subject to certain covenants. The Revolver expires and the Term Loan matures on September 27, 2018. During the years ended December 31, 2017 and 2016 , the Company made repayments of $107.6 million and $47.5 million respectively, plus accrued interest. The aforementioned payments include additional payments made by the Company of $100.0 million and $40.0 million respectively, on the Term Loan and Revolver, which were in addition to the scheduled amounts due. The Company used cash and cash equivalents to fund the payments. As of December 31, 2017 , there was no outstanding balance on the Revolver, and the Company had availability of $149.3 million on the Revolver. As of December 31, 2017 , $78.0 million was outstanding under the Term Loan. The Company anticipates that the Revolver and Term Loan will be retired in 2018. The borrowing rate on both its Term Loan and Revolver are derived from the one month LIBOR, and based on the Company's leverage ratio as of December 31, 2017 , the effective interest rate on its borrowings is equal to 2.57% . Interest expense for the years ended December 31, 2017 and 2016 are presented within the "Other, net" section of the Consolidated Statements of Income and expenses associated with the Term Loan and Revolver were $3.0 million and $3.5 million , respectively. The Credit Agreement contains customary representations and warranties and certain covenants that place certain limitations on the Company. As of December 31, 2017 , the Company was in compliance with its covenants under the Credit Agreement. Interest Rate Swap On October 1, 2014, the Company entered into an interest rate swap transaction with a bank (the “Counterparty”). The Counterparty is among the syndicate of lenders under the existing Credit Agreement entered into on September 27, 2013. The Company entered into the interest rate swap transaction to mitigate the Company’s floating rate interest risk on an aggregate of $150 million of the Company’s debt that is currently outstanding under the Credit Agreement. The interest rate swap had an effective date of July 31, 2015 and a termination date of September 27, 2018 (which is the expiration date of the Credit Agreement). The Company is required to make certain monthly fixed rate payments to the Counterparty calculated on a notional amount of $150 million for the rate swap, while the Counterparty is obligated to make monthly floating rate payments to the Company referencing the same notional amount. The interest rate swap transaction has the effect of fixing the annual interest rate payable on $150 million of the Company’s outstanding debt under its existing credit facility to 1.89% , as of the effective date. The notional amounts of the interest rate swap agreement are used to measure interest to be paid or received and do not represent the amount of exposure to credit loss. This derivative instrument has been designated as a cash flow hedge of the variable interest payments on the related debt. Interest expenses are netted within the “Other, net” section of the Condensed Consolidated Statements of Income, and expenses associated with the interest rate swap were $1.3 million and $2.1 million for the years ended December 31, 2017 and 2016, respectively. Notwithstanding the terms of the interest rate swap transaction, the Company is ultimately obligated for all amounts due and payable under its existing Credit Agreement. The notional amount of the Company's derivative instruments are as follows: December 31, 2017 December 31, 2016 December 31, 2015 Interest Rate swap $ 150,000,000 $ 150,000,000 $ 150,000,000 The following table sets forth financial assets and liabilities measured at fair value in the consolidated balance sheets and the respective pricing levels to which the fair value measurements are classified within the fair value hierarchy. The Company uses the market approach to derive the value of its level 2 fair value measurements. Interest rate swaps are valued using publicized swap curves. Fair Value Measurements Quoted Prices with Other Observable Inputs (Level 2) December 31, 2017 December 31, 2016 December 31, 2015 Financial assets: Interest Rate Swap Asset $ — $ — $ — Financial Liabilities: Interest Rate Swap Liability (Other Accrued Liabilities) $ 230,845 $ 1,841,970 $ 2,947,438 Based on loan balances as of December 31, 2017 and the effective date of July 31, 2015 of the interest rate swap, a one percent increase in the Company's borrowing rate would increase net interest expense paid by the Company on its borrowings by less than $0.1 million on an annual basis.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES The provision for income taxes is based on the earnings reported in the accompanying consolidated financial statements. The Company recognizes deferred income tax liabilities and assets for the expected future tax consequences of events that have been included in the consolidated financial statements or tax returns. Under this method, deferred income tax liabilities and assets are determined based on the cumulative temporary differences between the financial statement and tax basis of assets and liabilities using enacted tax rates expected to apply taxable income in years which those temporary differences are expected to be recovered or settled. Deferred income tax expense is measured by the net change in deferred income tax assets and liabilities during the year. On December 22, 2017, President Trump signed into law the Tax Cuts and Jobs Act (the “Act”), a tax reform bill which, among other items, reduces the current federal income tax rate to 21% from 35%. The rate reduction is effective January 1, 2018, and is permanent. The Act has caused the Company’s deferred income taxes to be revalued. As changes in tax laws or rates are enacted, deferred tax assets and liabilities are adjusted through income tax expense. Pursuant to the guidance within SEC Staff Accounting Bulletin No. 118 (“SAB 118”), as of December 31, 2017, the Company recognized the provisional effects of the enactment of the Act for which measurement could be reasonably estimated. Although the Company continues to analyze certain aspects of the Act and refine its assessment, the ultimate impact of the Act may differ from these estimates due to its continued analysis or further regulatory guidance that may be issued as a result of the Act. Pursuant to SAB 118, adjustments to the provisional amounts recorded by the Company as of December 31, 2017 that are identified within a subsequent measurement period of up to one year from the enactment date will be included as an adjustment to tax expense from continuing operations in the period the amounts are determined. As a result of the reduction of the federal corporate income tax rate, the Company reduced the value of its net deferred tax liability by $38.4 million which was recorded as a reduction to income tax expense during the fourth quarter of 2017. The Company’s revaluation of its net deferred tax liability is subject to further refinement as additional information becomes available and further analysis is completed. The foreign components of income before the provision for income taxes were not material as of December 31, 2017 , 2016 and 2015 . The components of the provision for income taxes are as follows: 2017 2016 2015 Currently payable: Federal $ 133,166,194 $ 136,124,497 $ 129,379,597 State 3,984,000 3,805,000 2,908,000 Foreign 2,440,000 540,000 276,000 Total 139,590,194 140,469,497 132,563,597 Deferred income tax (benefit) expense: Primarily federal (14,585,412 ) 22,500,000 12,558,000 Provision for income taxes $ 125,004,782 $ 162,969,497 $ 145,121,597 The currently payable provision is further reduced by the tax benefits associated with the exercise, vesting or disposition of stock under the stock plans described in Note 5 . These reductions totaled approximately $8.3 million , $11.8 million and $5.0 million in 2017 , 2016 and 2015 , respectively. As a result of the implementation of ASU 2016-09 in first quarter 2017, as further discussed in Note 1 , this reduction was recognized through income tax expense in 2017, whereas the reductions were recognized as an adjustment of additional paid-in capital for the years 2016 and 2015. The effective income tax rates are different from the statutory federal income tax rates for the following reasons: 2017 2016 2015 Statutory federal income tax rate 35.00 % 35.00 % 35.00 % State income taxes, net of federal income tax benefit 0.50 0.50 0.40 Domestic production exclusion (2.80 ) (2.70 ) (2.80 ) Research tax credit (0.80 ) (0.80 ) (0.80 ) Increase (Reduction) in Reserve for Uncertain Tax Provisions 0.10 (0.20 ) (0.60 ) Change in Tax Rate on Deferred Taxes (7.20 ) — — Foreign Tax Credit (0.80 ) — — Other (0.50 ) 0.10 0.10 Effective income tax rate 23.50 % 31.90 % 31.30 % The tax effect of temporary differences which give rise to deferred income tax assets and liabilities at December 31, 2017 and 2016 , are as follows: December 31, 2017 2016 Assets: Accruals not currently deductible $ 4,546,767 $ 4,282,470 Stock based compensation 8,594,640 18,701,361 Other 3,679,680 3,924,945 Total deferred income tax assets 16,821,087 26,908,776 Liabilities: Excess tax over book depreciation (46,123,681 ) (65,642,206 ) Goodwill (18,972,334 ) (23,225,969 ) Unrealized gain on investments (2,093,105 ) (1,435,322 ) Intangible assets (4,172,726 ) (5,368,886 ) Other (4,347,885 ) (2,449,012 ) Net deferred income taxes $ (58,888,644 ) $ (71,212,619 ) Net current and non-current tax assets and liabilities are included in the consolidated balance sheets as follows: December 31, 2017 2016 Long-term assets 16,821,087 26,908,776 Long-term liabilities (75,709,731 ) (98,121,395 ) Total deferred tax liability $ (58,888,644 ) $ (71,212,619 ) Income taxes paid in cash were approximately $126.0 million , $144.1 million and $138.0 million in 2017 , 2016 and 2015 , respectively. The Tax Cuts and Jobs Act, along with reducing the federal income tax rate to 21% from 35%, implements a modified territorial system that provides for an exemption for foreign dividends. However, a one-time transition tax is payable in respect of cumulative retained earnings of foreign subsidiaries at a rate of 15.5% for earnings represented by cash or cash equivalents and 8.0% for the balance of such earnings. The Company does not anticipate the one-time transition tax, the provisional estimate of which is $1.2 million , to be material. The Company follows the provisions of the Financial Accounting Standards Codification 740 (“ASC 740”), “Income Taxes.” A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: 2017 2016 2015 Beginning of year $ 3,408,000 $ 5,375,000 $ 8,288,000 Additions based on tax positions related to the current year 941,000 756,000 1,765,000 Additions for tax positions in prior years 289,000 487,000 428,000 Reductions for tax positions in prior years (63,000 ) (2,949,000 ) (336,000 ) Reductions as a result of completed audit examinations — — (4,162,000 ) Reductions as a result of a lapse of the applicable statute of limitations (140,000 ) (261,000 ) (608,000 ) End of year $ 4,435,000 $ 3,408,000 $ 5,375,000 If recognized, unrecognized tax benefits would affect the effective tax rate. The Company recognizes interest and penalties related to unrecognized tax benefits through the provision for income taxes. The Company has accrued approximately $433,000 and $277,000 for interest as of December 31, 2017 and 2016 , respectively. Interest recorded during 2017 , 2016 and 2015 was not considered significant. The Company is also subject to periodic and routine audits in both domestic and foreign tax jurisdictions, and it is reasonably possible that the amounts of unrecognized tax benefits could change as a result of an audit. Based on the current audits in process, the payment of taxes as a result of audit settlements, and the completion of tax examinations, the Company does not expect these to have a material impact on the Company’s financial position or results of operations. For the majority of tax jurisdictions, the Company is no longer subject to U.S. federal, state and local, or non-U.S. income tax examinations by tax authorities for years before 2012.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Employee Benefit Plan	EMPLOYEE BENEFIT PLAN The Company has a 401(k) retirement savings plan in which substantially all of its employees may participate. The plan includes a provision for the Company to match a percentage of the employee’s contributions at a rate determined by the Company’s Board of Directors. In 2017 , 2016 and 2015 the Company’s contributions were approximately $7.7 million , $6.5 million and $5.7 million , respectively. The increase in each of the years was due to increased employee participation in the plan. The Company does not provide health care benefits to retired employees.

Stock-Based Compensation Plans

Stock-Based Compensation Plans	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation Plans	STOCK-BASED COMPENSATION PLANS At December 31, 2017 , the Company had four equity incentive plans which include two stock option plans, a restricted stock plan and an employee stock purchase plan. All of the plans and any material amendments thereto have previously been approved by shareholders. Employee Stock Option Plan In May 2014, the Employee Stock Option Plan was approved by shareholders, amending and restating a prior plan. The Company may grant up to 24,000,000 shares of common stock under the plan. The purpose of the plan is to provide an opportunity to use stock options as a means of recruiting new managerial and technical personnel and as a means for retaining certain employees of the Company by allowing them to purchase shares of common stock of the Corporation and thereby have an additional incentive to contribute to the prosperity of the Company. The Company has granted options on 11,404,018 shares (net of shares from canceled/expired options) under the plan through December 31, 2017 . Under the plan, the option exercise price equals the stock’s market price on date of grant. The options vest after one to five years, and expire after five to seven years. The fair value of each option grant in the Employee Stock Option Plan was estimated on the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions for the indicated periods: 2017 2016 2015 Dividend yield (1) 2.1 % 2.2 % 2.1 % Expected volatility (2) 26.7 % 33.2 % 35.8 % Risk-free interest rate (3) 2.0 % 1.4 % 1.5 % Expected term of options (in years) (4) 4.2 4.7 4.3 Weighted-average grant-date fair value $ 4 $ 4 $ 4 (1) Represents the Company's estimated cash dividend yield over the expected term of option grant. (2) Amount is determined based on analysis of historical price volatility of the Company's common stock. The expected volatility is based on the daily percentage change in the price of the stock over a period equal to the expected term of the option grant. (3) Represents the U.S. Treasury yield over the expected term of the option grant. (4) Represents the period of time that options granted are expected to be outstanding. Based on analysis of historical option exercise activity, the Company has determined that all employee groups exhibit similar exercise and post-vesting termination behavior. As of December 31, 2017 , there was $9,957,103 of unrecognized compensation cost related to share-based payments which is expected to be recognized over the remaining vesting periods, with a weighted-average period of 1.8 years. A summary of the status of the Company’s employee stock option plan at December 31, 2017 , 2016 and 2015 , and changes during the same periods are presented in the tables and narrative below. 2017 Shares (000) Wtd. Avg. Ex. Price Wtd. Avg. Remaining Contract Life Aggregate Intrinsic Value (000) Outstanding at Beginning of Year 14,252 $ 15 Granted 1,295 20 Exercised (3,476 ) 13 $ 25,156 Forfeited (234 ) 16 Outstanding at End of Year 11,837 16 2.7 Yrs $ 58,202 Exercisable at End of Year 5,297 $ 15 2 Yrs $ 32,152 2016 Shares (000) Wtd. Avg. Ex. Price Wtd. Avg. Remaining Contract Life Aggregate Intrinsic Value (000) Outstanding at Beginning of Year 17,692 $ 14 Granted 3,227 17 Exercised (6,291 ) 12 $ 31,790 Forfeited (376 ) 15 Outstanding at End of Year 14,252 15 3 Yrs $ 67,763 Exercisable at End of Year 4,855 $ 14 2.3 Yrs $ 30,021 2015 Shares (000) Wtd. Avg. Ex. Price Wtd. Avg. Remaining Contract Life Aggregate Intrinsic Value (000) Outstanding at Beginning of Year 17,829 $ 13 Granted 2,966 17 Exercised (2,344 ) 12 $ 11,596 Forfeited (759 ) 14 Outstanding at End of Year 17,692 14 3 Yrs $ 45,842 Exercisable at End of Year 6,858 $ 13 2.1 Yrs $ 23,917 A summary of the status of the Company’s non-vested employee stock option activity for the years ended December 31, 2017 , 2016 , and 2015 , are presented in the table and narrative below: 2017 2016 2015 Shares (000) Wtd. Avg Grant Date Fair Value Shares (000) Wtd. Avg Grant Date Fair Value Shares (000) Wtd. Avg Grant Date Fair Value Nonvested Stock Options at Beginning of Year 9,397 $ 4 10,835 $ 4 13,265 $ 4 Granted 1,295 4 3,227 4 2,966 4 Vested (3,941 ) 4 (4,343 ) 4 (4,678 ) 4 Forfeited (211 ) 4 (322 ) 4 (718 ) 4 Nonvested Stock Options at End of Year 6,540 $ 4 9,397 $ 4 10,835 $ 4 Non-employee Director Stock Option Plan In 2012, an Amended and Restated Non-employee Director Stock Option Plan, covering a total of 1,000,000 shares of common stock, was approved by shareholders replacing a prior plan. The Company has granted options on 427,000 shares (net of shares from canceled options) under the new director plan and 1,074,480 shares (net of shares from canceled options) under a prior plan through December 31, 2017 . Under the shareholder approved plans, the option exercise price equals the stock's market price on date of grant. The options vest after six months, and expire after ten years. The fair value of each option grant in the Non-employee Director Stock Option Plans was estimated on the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions for the indicated periods: 2017 2016 2015 Dividend yield (1) 2.2 % 2.2 % 2.1 % Expected volatility (2) 28.3 % 34.1 % 36.3 % Risk-free interest rate (3) 2.2 % 1.9 % 2.2 % Expected term of options (in years) (4) 6.4 6.2 6.0 Weighted-average grant-date fair value $ 5 $ 4 $ 5 (1) Represents the Company's estimated cash dividend yield over the expected term of option grant. (2) Amount is determined based on analysis of historical price volatility of the Company's common stock. The expected volatility is based on the daily percentage change in the price of the stock over a period equal to the expected term of the option grant. (3) Represents the U.S. Treasury yield over the expected term of the option grant. (4) Represents the period of time that options granted are expected to be outstanding. Based on analysis of historical option exercise activity, the Company has determined that non-employee directors exhibit similar exercise and post-vesting termination behavior. As of December 31, 2017 , there were no unrecognized compensation costs related to share-based payments under this plan. A summary of the status of the Company’s Non-employee Director Stock Option Plan at December 31, 2017 , 2016 , and 2015 , and changes during the same periods are presented in the tables and narrative below: 2017 Shares (000) Wtd. Avg. Ex. Price Wtd. Avg. Remaining Contract Life Aggregate Intrinsic Value (000) Outstanding at Beginning of Year 381 $ 14 Granted 56 19 Exercised (31 ) 14 Forfeited — — Outstanding at End of Year 406 15 6.1 Yrs $ 2,565 Exercisable at End of Year 406 $ 15 6.1 Yrs $ 2,565 2016 Shares (000) Wtd. Avg. Ex. Price Wtd. Avg. Remaining Contract Life Aggregate Intrinsic Value (000) Outstanding at Beginning of Year 373 $ 13 Granted 56 16 Exercised (36 ) 10 Forfeited (12 ) 16 Outstanding at End of Year 381 14 6.4 Yrs $ 2,180 Exercisable at End of Year 381 $ 14 6.4 Yrs $ 2,180 2015 Shares (000) Wtd. Avg. Ex. Price Wtd. Avg. Remaining Contract Life Aggregate Intrinsic Value (000) Outstanding at Beginning of Year 381 $ 12 Granted 49 17 Exercised (57 ) 11 Forfeited — — Outstanding at End of Year 373 13 6.4 Yrs $ 1,069 Exercisable at End of Year 373 $ 13 6.4 Yrs $ 1,069 A summary of the status of the Company’s nonvested Non-employee Director Stock Option Plan activity for the years ended December 31, 2017 , 2016 , and 2015 , are presented in the table and narrative below: 2017 2016 2015 Shares (000) Wtd. Avg Grant Date Fair Value Shares (000) Wtd. Avg Grant Date Fair Value Shares (000) Wtd. Avg Grant Date Fair Value Nonvested Stock Options at Beginning of Year — $ — — $ — — $ — Granted 56 5 56 4 49 5 Vested (56 ) 5 (56 ) 4 (49 ) 5 Forfeited — — — — — — Nonvested stock options at End of Year — $ — — $ — — $ — Employee Stock Purchase Plan In 2013, the Gentex Corporation Employee Stock Purchase Plan covering 2,000,000 shares of common stock was approved by the shareholders, replacing a prior plan. Under such plan, the Company sells shares at 85% of the stock’s market price at date of purchase. Under ASC 718, the 15% discounted value is recognized as compensation expense. The following table summarizes shares sold to employees under the 2013 Plan in the years ended December 31, 2017 , 2016 and 2015 . Plan 2017 2016 2015 Cumulative Shares Issued in 2017 Weighted Average Fair Value 2017 2013 Employee Stock Purchase Plan 175,479 177,781 201,785 794,997 $ 17.12 Restricted Stock Plan In 2015, an amendment to the Company’s Second Restricted Stock Plan was approved by shareholders. The Plan amendment increased the maximum number of shares that may be subject to awards to 9,000,000 shares and to extend the Plan’s termination date to February 19, 2025. The purpose of this plan is to permit grants of shares, subject to restrictions, to employees of the Company as a means of retaining and rewarding them for performance and to increase their ownership in the Company. Shares awarded under the plan entitle the shareholder to all rights of common stock ownership except that the shares may not be sold, transferred, pledged, exchanged or otherwise disposed of during the restriction period. The restriction period is determined by a committee, appointed by the Board of Directors, but may not exceed ten years. The Company has 2,019,404 shares outstanding and has issued 5,334,225 shares under the plan as of December 31, 2017 . During 2017 , 2016 , and 2015 , 228,630 , 246,660 and 229,660 shares, respectively, were granted with a restriction period of five years, and 628,015 during 2017 with a restriction of four years, and cliff vest after the restriction period with no additional restrictions, at market prices ranging from $18.97 to $21.33 in 2017 , $14.70 to $19.69 in 2016 , and $15.50 to $18.30 in 2015 , and has unearned stock-based compensation of $22,417,962 associated with these restricted stock grants. The unearned stock-based compensation related to these grants is being amortized to compensation expense over the applicable restriction periods. Amortization expense of restricted stock for years ended December 31, 2017 , 2016 and 2015 was $5,353,339 , $3,885,042 , and $3,486,242 respectively.

Contingencies

Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Contingencies	CONTINGENCIES The Company is periodically involved in legal proceedings, legal actions and claims arising in the normal course of business, including proceedings relating to product liability, intellectual property, safety and health, employment and other matters. Such matters are subject to many uncertainties and outcomes are not predictable. The Company does not believe, however, that at the current time there are matters that constitute material pending legal proceedings that will have a material adverse effect on the financial position or future results of operations of the Company.

Segment Reporting

Segment Reporting	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Reporting	SEGMENT REPORTING ASC 280, “Disclosures About Segments of an Enterprise and Related Information,” requires that a public enterprise report financial and descriptive information about its reportable operating segments subject to certain aggregation criteria and quantitative thresholds. Operating segments are defined by ASC 280 as components of an enterprise about which separate financial information is available that is evaluated regularly by the chief operating decision-makers in deciding how to allocate resources and in assessing performance. 2017 2016 2015 Revenue: Automotive Products United States $ 567,492,812 $ 554,945,912 $ 494,876,354 Germany 351,123,204 328,208,190 295,044,988 Japan 185,261,067 154,005,299 148,632,237 Other Countries 654,250,385 602,532,841 568,318,425 Other 36,745,110 39,232,514 36,745,702 Total $ 1,794,872,578 $ 1,678,924,756 $ 1,543,617,706 Income (Loss) from Operations: Automotive Products $ 512,895,699 $ 497,753,966 $ 445,067,511 Other 10,462,653 13,988,969 13,698,928 Total $ 523,358,352 $ 511,742,935 $ 458,766,439 Assets: Automotive Products $ 1,472,061,650 $ 1,457,989,335 $ 1,414,426,679 Other 9,576,514 9,384,154 9,429,994 Corporate 870,415,748 842,246,344 724,816,255 Total $ 2,352,053,912 $ 2,309,619,833 $ 2,148,672,928 Depreciation & Amortization: Automotive Products $ 95,378,100 $ 86,567,248 $ 78,925,332 Other 300,935 290,296 306,908 Corporate 3,891,873 1,729,886 1,366,927 Total $ 99,570,908 $ 88,587,430 $ 80,599,167 Capital Expenditures: Automotive Products $ 82,703,576 $ 99,811,083 $ 97,632,519 Other 170,357 200,262 161,247 Corporate 21,166,986 20,944,269 147,996 Total $ 104,040,919 $ 120,955,614 $ 97,941,762 Other includes Dimmable Aircraft Windows and Fire Protection Products. Major product line revenues included within these segments are as follows: 2017 2016 2015 Automotive Products Automotive Mirrors $ 1,573,222,820 $ 1,456,963,758 $ 1,332,791,398 HomeLink ® Modules* 184,904,648 182,728,485 174,080,606 Total Automotive Products $ 1,758,127,468 $ 1,639,692,243 $ 1,506,872,004 Other Products Revenue $ 36,745,110 $ 39,232,513 $ 36,745,702 Total Revenue $ 1,794,872,578 $ 1,678,924,756 $ 1,543,617,706 *Excludes HomeLink ® revenue integrated into automotive mirrors. Corporate assets are principally cash and cash equivalents, investments, deferred income taxes and corporate fixed assets. Substantially all long-lived assets are located in the U.S. Automotive Products revenues in the “Other” category are sales to customer automotive manufacturing plants in Korea, Mexico, Canada, Hungary, China, and the United Kingdom as well as other foreign automotive customers. Most of the Company’s non-U.S. sales are invoiced and paid in U.S. dollars. During the years ended December 31, 2017 , 2016 and 2015 , approximately 8% , 7% and 6% of the Company’s net sales were invoiced and paid in foreign currencies respectively. In 2017 , the Company had four automotive customers (including direct sales to OEM customers and sales through their Tier 1 suppliers), which individually accounted for 10% or more of net sales as follows: Toyota Motor Corporation Volkswagen Group Ford Motor Company Daimler AG 2017 12 % 15 % 10 % 10 % 2016 11 % 14 % 11 % # 2015 11 % 14 % 11 % # # - Less than 10 percent.

Quarterly Financial Information

Quarterly Financial Information (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information (Unaudited)	QUARTERLY FINANCIAL INFORMATION (UNAUDITED) The following table sets forth selected financial information for all of the quarters during the years ended December 31, 2017 and 2016 (in thousands, except per share data): First Second Third Fourth 2017 2016 2017 2016 2017 2016 2017 2016 Net Sales $ 453,535 $ 405,568 $ 443,139 $ 423,801 $ 438,628 $ 429,643 $ 459,570 $ 419,913 Gross Profit 175,801 158,691 167,208 166,773 171,230 173,822 180,290 169,167 Operating Income 134,427 120,849 125,865 128,746 129,073 134,212 133,994 127,936 Net Income 97,557 80,280 88,536 86,485 90,230 92,065 130,469 88,761 Earnings Per Share (Basic) $ 0.34 $ 0.28 $ 0.31 $ 0.30 $ 0.32 $ 0.32 $ 0.46 $ 0.31 Earnings Per Share (Diluted) $ 0.33 $ 0.28 $ 0.31 $ 0.30 $ 0.31 $ 0.32 $ 0.46 $ 0.31

Comprehensive Income

Comprehensive Income	12 Months Ended
	Dec. 31, 2017
Comprehensive Income [Abstract]
Comprehensive Income	COMPREHENSIVE INCOME Comprehensive income reflects the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. For the Company, comprehensive income represents net income adjusted for unrealized gains and losses on certain investments, foreign currency translation adjustments, and unrealized movement in derivative financial instruments designated as hedges. For the Twelve Months ended December 31, 2017 2016 2015 Foreign currency translation adjustments: Balance at beginning of period $ (2,862,999 ) $ (44,909 ) $ 1,403,899 Other comprehensive loss before reclassifications 3,508,029 (2,818,090 ) (1,448,808 ) Net current-period change 3,508,029 (2,818,090 ) (1,448,808 ) Balance at end of period 645,030 (2,862,999 ) (44,909 ) Unrealized gains (losses) on available-for-sale securities: Balance at beginning of period 2,788,975 829,907 10,868,322 Other comprehensive income (loss) before reclassifications 4,444,360 2,167,196 (5,513,842 ) Amounts reclassified from accumulated other comprehensive income (606,956 ) (208,128 ) (4,524,573 ) Net current-period change 3,837,404 1,959,068 (10,038,415 ) Balance at end of period 6,626,379 2,788,975 829,907 Unrealized gains (losses) on derivatives: Balance at beginning of period (1,197,281 ) (1,915,834 ) (959,206 ) Other comprehensive income (loss) before reclassifications 248,042 (672,419 ) (1,659,115 ) Amounts reclassified from accumulated other comprehensive income 871,213 1,390,972 702,487 Net current-period change 1,119,255 718,553 (956,628 ) Balance at end of period (78,026 ) (1,197,281 ) (1,915,834 ) Accumulated other comprehensive income (loss), end of period $ 7,193,383 $ (1,271,305 ) $ (1,130,836 ) All amounts are shown net of tax. Amounts in parentheses indicate debits. The following table presents details of reclassifications out of other comprehensive income for the twelve months ended December 31, 2017 , 2016 and 2015 . Details about Accumulated Other Comprehensive Income Components Affected Line item in the Statement of Consolidated Income For the Twelve Months ended December 31, 2017 2016 2015 Unrealized gains and (losses) on available-for-sale securities Realized gain on sale of securities $ 933,778 $ 320,197 $ 6,960,881 Other, net Provision for Income Taxes (326,822 ) (112,069 ) (2,436,308 ) Provision for Income Taxes Total reclassifications for the period $ 606,956 $ 208,128 $ 4,524,573 Net of tax Unrealized gains (losses) on derivatives Realized loss on interest rate swap $ (1,340,329 ) $ (2,139,958 ) $ (1,080,750 ) Other, net Provision for Income Taxes 469,116 748,986 378,263 Provision for Income Taxes $ (871,213 ) $ (1,390,972 ) $ (702,487 ) Net of tax Total reclassifications for the period $ (264,257 ) $ (1,182,844 ) $ 3,822,086 Net of tax

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	GOODWILL AND INTANGIBLE ASSETS The Company recorded Goodwill of $307.4 million related to the HomeLink ® acquisition, which occurred in September 2013. The carrying value of Goodwill as of December 31, 2017 and December 31, 2016 was $307.4 million as set forth in the table below. Carrying Amount Balance as of December 31, 2016 $ 307,365,845 Acquisitions — Divestitures — Impairments — Other — Balance as of December 31, 2017 $ 307,365,845 The Intangible Assets and related change in carrying values are set forth in the table below as of December 31, 2017 and December 31, 2016 . As of December 31, 2017 : Other Intangible Assets Gross Accumulated Amortization Net Assumed Useful Life HomeLink ® Trade Names and Trademarks $ 52,000,000 $ — $ 52,000,000 Indefinite HomeLink ® Technology 180,000,000 (63,750,000 ) $ 116,250,000 12 years Existing Customer Platforms 43,000,000 (18,275,000 ) $ 24,725,000 10 years Exclusive Licensing Agreement 96,000,000 — $ 96,000,000 Indefinite Total other identifiable intangible assets 371,000,000 (82,025,000 ) 288,975,000 As of December 31, 2016 : Other Intangible Assets Gross Accumulated Amortization Net Assumed Useful Life HomeLink ® Trade Names and Trademarks $ 52,000,000 $ — $ 52,000,000 Indefinite HomeLink ® Technology 180,000,000 (48,750,000 ) $ 131,250,000 12 years Existing Customer Platforms 43,000,000 (13,975,000 ) $ 29,025,000 10 years Exclusive Licensing Agreement 96,000,000 — $ 96,000,000 Indefinite Total other identifiable intangible assets 371,000,000 (62,725,000 ) 308,275,000 Accumulated amortization on patents and intangible assets was approximately $101.0 million and $79.2 million at December 31, 2017 and 2016 , respectively. Amortization expense on patents and other intangible assets was approximately $22.5 million , $22.3 million , and $22.5 million in 2017 , 2016 and 2015, respectively. At December 31, 2017 , patents had a weighted average amortized life of 10 years . Excluding the impact of any future acquisitions, the Company anticipates amortization expense including patents and other intangible assets for each of the years ended December 31, 2018, 2019, 2020, and 2021 to be approximately $22 million annually and approximately $21 million for the year ended December 31, 2022.

Summary of Significant Accoun19

Summary of Significant Accounting and Reporting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Consolidation	Consolidation The consolidated financial statements include the accounts of Gentex Corporation and all of its wholly-owned subsidiaries (together the “Company”). All significant intercompany accounts and transactions have been eliminated.
Cash Equivalents	Cash Equivalents Cash equivalents consist of funds invested in bank accounts and money market funds that have daily liquidity.
Allowance For Doubtful Accounts	Allowance For Doubtful Accounts The Company bases its allowances for doubtful accounts related to receivables on historical credit and collections experience, and the specific identification of other potential problems impacting collectability, including the economic climate. Actual collections can differ, requiring adjustments to the allowances. Individual accounts receivable balances are evaluated on a monthly basis, and those balances considered uncollectible are charged to the allowance. Collections of amounts previously written off are recorded as an increase to the allowance.
Investments	ASC 320, Accounting for Certain Investments in Debt and Equity Securities , as amended and interpreted, provides guidance on determining when an investment is other-than-temporarily impaired. The Company reviews its fixed income and equity investment portfolio for any unrealized losses that would be deemed other-than-temporary and require the recognition of an impairment loss in income. If the cost of an investment exceeds its fair value, the Company evaluates, among other factors, general market conditions, the duration and extent to which the fair value is less than cost, and the Company’s intent and ability to hold the investments. Management also considers the type of security, related-industry and sector performance, as well as published investment ratings and analyst reports, to evaluate its portfolio. Once a decline in fair value is determined to be other-than-temporary, an impairment charge is recorded and new cost basis in the investment is established. If market, industry, and/or investee conditions deteriorate, the Company may incur future impairments. Investments The Company follows the provisions of ASC 820, Fair Value Measurements and Disclosures, for its financial assets and liabilities, and for its non-financial assets and liabilities subject to fair value measurements. ASC 820 provides a framework for measuring the fair value of assets and liabilities. This framework is intended to provide increased consistency in how fair value determinations are made under various existing accounting standards that permit, or in some cases, require estimates of fair-market value. This standard also expanded financial statement disclosure requirements about a company’s use of fair-value measurements, including the effect of such measure on earnings. The cost of securities sold is based on the specific identification method. The Company’s common stocks and certain mutual funds are classified as available for sale and are stated at fair value based on quoted market prices, and as such are classified as Level 1 assets. The Company determines the fair value of its government securities, corporate bonds, and certain mutual funds by utilizing monthly valuation statements that are provided by its broker. The broker determines the investment valuation by utilizing the bid price in the market and also refers to third party sources to validate valuations, and as such are classified as Level 2 assets. The Company's certificates of deposit have remaining maturities of less than one year and are classified as available for sale, and are considered as Level 1 assets. These investments are carried at cost, which approximates fair value.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company’s financial instruments consist of cash and cash equivalents, investments, accounts receivable accounts payable, short and long term debt. The Company’s estimate of the fair values of these financial instruments approximates their carrying amounts at December 31, 2017 and 2016 .
Inventories	Inventories Inventories include material, direct labor and manufacturing overhead and are valued at the lower of first-in, first-out (FIFO) cost or market.
Plant and Equipment	Plant and Equipment Plant and equipment is stated at cost. Depreciation and amortization are computed for financial reporting purposes using the straight-line method, with estimated useful lives of 7 to 30 years for buildings and improvements, and 3 to 10 years for machinery and equipment.
Impairment or Disposal of Long-Lived Assets	Impairment or Disposal of Long-Lived Assets The Company reviews long-lived assets, including property, plant and equipment and other intangible assets with definite lives, for impairment whenever events or changes in circumstances indicate that the asset’s carrying amount may not be recoverable. The Company conducts its long-lived asset impairment analysis in accordance with ASC 360-10-15, Impairment or Disposal of Long-Lived Assets . ASC 360-10-15 requires the Company to group assets and liabilities at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities and evaluate the asset group against the sum of the undiscounted future cash flows. If the undiscounted cash flows do not indicate the carrying amount of the asset is recoverable, an impairment charge is measured as the amount by which the carrying amount of the asset group exceeds its fair value based on discounted cash flow analysis or appraisals.
Patents	Patents The Company’s policy is to capitalize costs incurred to obtain patents. The cost of patents is amortized over their useful lives. The cost of patents in process is not amortized until issuance. The Company periodically obtains intellectual property rights, in the ordinary course of business, and the cost of the rights are amortized over their useful lives.
Goodwill and Other Intangible Assets	Goodwill and Intangible Assets Goodwill reflects the cost of an acquisition in excess of the fair values assigned to identifiable net assets acquired. The Company reviews goodwill for impairment during the fourth quarter on an annual basis or more frequently if events or changes in circumstances indicate that goodwill might be impaired. The Company performs an impairment review for its automotive reporting unit, which has been determined to be one of the Company’s reportable segments using a fair value method which incorporates management’s judgments and assumptions, as well as incorporates third party valuations. The fair value of a reporting unit refers to the price that would be received to sell the unit as a whole in an orderly transaction between market participants at the measurement date. In estimating the fair value, the Company uses a combination of widely accepted valuation methodologies incorporating certain judgments and assumptions to arrive at the fair value of the reporting unit. The assumptions included in the impairment tests require judgment and changes to these inputs could impact the results of the calculations which could result in an impairment charge in future periods if the carrying amount of the reporting unit exceeds its calculated fair value. Other than management's internal projections of future cash flows, the primary assumptions used in the step 1 and step 2 impairment tests are the weighted-average cost of capital and long-term growth rates. Although the Company's cash flow forecasts are based on assumptions that are considered reasonable by management and consistent with the plans and estimates management is using to operate the underlying business, there are significant judgments in determining the expected future cash flows attributable to a reporting unit. There have been no impairment charges booked currently or in prior periods in which goodwill existed. Indefinite lived intangible assets are also subject to annual impairment testing or more frequently if indicators of impairment are identified. Management judgment and assumptions are required in determining the underlying fair value of the indefinite lived intangible assets. While the Company believes the judgments and assumptions used in determining fair value are reasonable, different assumptions could change the estimated fair values and, therefore, impairment charges could be required, which could be material to the consolidated financial statements. The indefinite lived intangible assets were not impaired as a result of the annual test prepared by management for either period presented.
Revenue Recognition	Revenue Recognition The Company’s revenue is generated from sales of its products. Sales are recognized when the product is shipped and legal title has passed to the customer. The Company does not generate sales from arrangements with multiple deliverables. Effective January 1, 2018, the Company adopted ASC Topic 606, Revenue from Contracts with Customers , using the modified retrospective method. This guidance supersedes nearly all existing revenue recognition guidance under US GAAP. The core principle of the guidance is that an entity should recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The Company has drafted its accounting policy for the new standard based on a detailed review of its business and contracts. Based on the new guidance, the Company expects to continue recognizing revenue at a particular point in time for the majority of its contracts with customers, which is generally when products are either shipped or delivered, and therefore the adoption of the standard did not have a material impact on its consolidated financial statements.
Advertising and Promotional Materials	Advertising and Promotional Materials All advertising and promotional costs are expensed as incurred
Repairs and Maintenance	Repairs and Maintenance Major renewals and improvements of property and equipment are capitalized, and repairs and maintenance are expensed as incurred.
Self-Insurance	Self-Insurance The Company is self-insured for a portion of its risk on workers’ compensation and employee medical costs. The arrangements provide for stop loss insurance to manage the Company’s risk. Operations are charged with the cost of claims reported and an estimate of claims incurred but not reported, based upon historical claims lag information and other data.
Product Warranty	Product Warranty The Company periodically incurs product warranty costs. Any liabilities associated with product warranty are estimated based on known facts and circumstances and are not significant at December 31, 2017 , 2016 and 2015 . The Company does not offer extended warranties on its products.
Income Taxes	Income Taxes The provision for income taxes is based on the earnings reported in the consolidated financial statements. Deferred income tax assets and liabilities are computed for differences between the financial statement and tax basis of assets and liabilities that will result in taxable or deductible amounts in the future. Such deferred income tax asset and liability computations are based on enacted tax laws and rates.
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) Comprehensive income (loss) reflects the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. For the Company, comprehensive income represents net income adjusted for unrealized gains and losses on certain investments, unrealized gains and losses on certain derivative financial instruments, and foreign currency translation adjustments that are further detailed in Note 9 to the Consolidated Financial Statements.
Foreign Currency Translation	Foreign Currency Translation The financial position and results of operations of the Company’s foreign subsidiaries are measured using the local currency as the functional currency. Assets and liabilities are translated at the exchange rate in effect at year-end. Income statement accounts are translated at the average rate of exchange in effect during the year. The resulting translation adjustment is recorded as a separate component of shareholders’ investment. Gains and losses arising from re-measuring foreign currency transactions into the appropriate currency are included in the determination of net income.
Derivative Financial Instruments	Derivative Financial Instruments The Company accounts for derivative financial instruments in accordance with the guidance provided in ASC Topic 815, Derivatives and Hedging. The guidance requires that all derivative instruments be recognized as assets or liabilities on the consolidated balance sheets and measured at fair value. For derivatives designated as cash flow hedges, fair value changes in the effective portion of the hedging instrument are recognized in accumulated other comprehensive income on the consolidated balance sheets until the forecasted transaction affects earnings of the consolidated entity. Any ineffective portion of the fair value change is recognized in earnings immediately. The Company reported a loss of $.1 million in earnings for the year ended December 31, 2017 as a result of the ineffectiveness of the hedge. As of December 31, 2016, there was no ineffectiveness. The Company seeks to reduce exposure to interest rate fluctuations through the use of an interest rate swap agreement. The Company does not buy and sell such financial instruments for investment or speculative purposes. The Company is exposed to credit loss in the event of nonperformance by the counterparties on derivative contracts. It is the Company’s practice to manage its credit risk on these transactions by dealing with highly rated financial institutions.
Stock-Based Compensation Plans	Stock-Based Compensation Plans The Company accounts for stock-based compensation using the fair value recognition provisions of ASC 718, “Compensation - Stock Compensation.” As described more fully in Note 5, the Company provides compensation benefits under two stock option plans, a restricted stock plan and an employee stock purchase plan.
Estimates	Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Recent Accounting Standards	Recent Accounting Standards In March 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-09, Improvements to Employee Share-Based Payment Accounting , which amends Accounting Standards Codification (ASC) Topic 718, Compensation - Stock Compensation . ASU 2016-09 simplifies several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. Under previous guidance, excess tax benefits and deficiencies from stock-based compensation arrangements were recorded in equity when the awards vested or were settled. ASU 2016-09 requires prospective recognition of excess tax benefits and deficiencies in the income statement as a component of the income tax provision. In addition, under ASU 2016-09, excess income tax benefits from stock-based compensation arrangements are classified as cash flow from operations, rather than as cash flow from financing activities. ASU 2016-09 also allows for the Company to make an entity-wide accounting policy election to either estimate the number of awards that are expected to vest or account for forfeitures when they occur. The Company will continue to apply its existing entity-wide policy to estimate the number of awards expected to be forfeited. The Company adopted this standard in the first quarter of 2017. Impact to Consolidated Statements of Income One of the more significant impacts of adopting ASU 2016-09 is the required change in how the Company recognizes the excess tax benefits or deficiencies related to share-based compensation. For example, prior to adopting ASU 2016-09 such benefits and deficiencies were credited or charged, respectively, to additional paid-in capital in the Company’s Consolidated Balance Sheets. Under ASU 2016-09, these benefits and deficiencies are recognized as a discrete tax benefit or discrete tax expense, in the Company’s Consolidated Statements of Income. For the years ended December 31, 2017, the Company recognized a net discrete tax benefit of $5.2 million , related to net tax benefits from share-based compensation. ASU 2016-09 requires companies to adopt the amendment related to accounting for benefits and deficiencies on a prospective basis only. As a result, no change has been made to the Consolidated Statements of Income for the years ended December 31, 2016 and 2015 related to the $3.2 million and $1.2 million of net tax benefits the Company recognized as additional paid-in capital during each respective period. Net tax benefits of $3.2 million recognized as additional paid-in-capital during the year ended December 31, 2016 includes gross tax benefits of $4.9 million net of $1.7 million tax expense. Net tax benefits of $1.2 million recognized as additional paid-in-capital during the year ended December 31, 2015 includes gross tax benefits of $1.7 million net of $.5 million tax expense. In consideration of the impact of the adoption of this standard to earnings per share, the total impact of adoption of this standard to the earnings per share calculation was less than $.02 for the year ending December 31, 2017. Impact to Consolidated Statements of Cash Flows In addition to the income tax consequences described above, under ASU 2016-09 all tax benefits related to share-based payments are reported as cash flows from operating activities along with all other income tax cash flows. Previously, tax benefits from share-based payment arrangements were reported as cash flows from financing activities. With respect to the classification of tax benefits on the statement of cash flows, ASU 2016-09 allows companies to elect either a prospective or retrospective application. The Company has elected to apply this classification amendment retrospectively. As a result, the Company elected to reclassify $5.6 million of tax expense previously reported as cash flows from financing activities on the Company’s Consolidated Statement of Cash Flows for the twelve months ended December 31, 2016 as cash flows from operating activities. Effective January 1, 2018, the Company adopted ASC Topic 606, Revenue from Contracts with Customers , using the modified retrospective method. This guidance supersedes nearly all existing revenue recognition guidance under US GAAP. The core principle of the guidance is that an entity should recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The Company has drafted its accounting policy for the new standard based on a detailed review of its business and contracts. Based on the new guidance, the Company continues to recognize revenue at a particular point in time for the majority of its contracts with customers, which is generally when products are either shipped or delivered. Therefore, the adoption of ASC 606 did not have a material impact on the consolidated financial statements. The Company anticipates it will expand its consolidated financial statement disclosures in order to comply with the disclosure requirements of the ASU beginning in the first quarter of 2018. Effective January 1, 2018, the Company adopted ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilitie s. The standard amends various aspects of the recognition, measurement, presentation, and disclosure of financial instruments. The most significant impact to our consolidated financial statements relates to the recognition and measurement of equity investments at fair value with changes recognized in Net income. The amendment also updates certain presentation and disclosure requirements. The Company will have a cumulative-effect adjustment in the first quarter of 2018 of approximately $7 million as a result of the implementation of this guidance, as a result of the reclassification of the net unrealized gain for available-for-sale securities as of December 31, 2017 from other comprehensive income to retained earnings. The adoption of ASU 2016-01 is expected to increase volatility in net income as changes in the fair value of available-for-sale equity investments and changes in observable prices of equity investments without readily determinable fair values will be recorded in net income. In February 2016, the FASB issued ASU 2016-02, Leases , which provides guidance for lease accounting. The new guidance contained in the ASU stipulates that lessees will need to recognize a right-of-use asset and a lease liability for substantially all leases (other than leases that meet the definition of a short-term lease). The liability will be equal to the present value of lease payments. Treatment in the consolidated statements of earnings will be similar to the current treatment of operating and capital leases. The new guidance is effective on a modified retrospective basis for the Company in the first quarter of its fiscal year ending December 31, 2019. The Company is currently in the process of evaluating the impact of adoption of this standard on its consolidated financial statements.

Summary of Significant Accoun20

Summary of Significant Accounting and Reporting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Schedule of Allowance For Doubtful Accounts	The following table presents the activity in the Company’s allowance for doubtful accounts: Beginning Balance Net Additions/ (Reductions) to Costs and Expenses Deductions and Other Adjustments Ending Balance Year Ended December 31, 2017: Allowance for Doubtful Accounts $ 2,917,424 $ — $ (202,891 ) $ 2,714,533 Year Ended December 31, 2016: Allowance for Doubtful Accounts $ 2,663,477 $ — $ 253,947 $ 2,917,424 Year Ended December 31, 2015: Allowance for Doubtful Accounts $ 2,711,248 $ — $ (47,771 ) $ 2,663,477
Schedule of Assets or Liabilities Having Recurring Measurements	Assets or liabilities that have recurring fair value measurements are shown below as of December 31, 2017 and December 31, 2016 : Fair Value Measurements at Reporting Date Using Total as of Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Description December 31, 2017 (Level I) (Level 2) (Level 3) Cash & Cash Equivalents $ 569,734,496 $ 569,734,496 $ — $ — Short-Term Investments: Certificate of Deposit 130,000,000 130,000,000 — — Government Securities 9,011,130 — 9,011,130 — Mutual Funds 393,581 — 393,581 — Corporate Bonds 12,944,999 — 12,944,999 — Other 188,344 188,344 — — Long-Term Investments: Corporate Bonds 3,018,720 — 3,018,720 — Common Stocks 15,703,371 15,703,371 — — Mutual Funds 34,681,337 34,681,337 — — Preferred Stock 1,178,991 1,178,991 — — Total $ 776,854,969 $ 751,486,539 $ 25,368,430 $ — Fair Value Measurements at Reporting Date Using Total as of Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Description December 31, 2016 (Level I) (Level 2) (Level 3) Cash & Cash Equivalents $ 546,477,075 $ 546,477,075 $ — $ — Short-Term Investments: Certificate of Deposit 130,000,000 130,000,000 — — Government Securities 13,993,480 — 13,993,480 — Mutual Funds 26,116,681 — 26,116,681 — Corporate Bonds 6,698,382 — 6,698,382 — Other 212,653 212,653 — — Long-Term Investments: Corporate Bonds 1,948,556 — 1,948,556 — Common Stocks 12,849,007 12,849,007 — — Mutual Funds 28,872,010 28,872,010 — — Preferred Stock 714,000 714,000 — — Government Securities 5,510,790 — 5,510,790 — Total $ 773,392,634 $ 719,124,745 $ 54,267,889 $ —
Schedule of Amortized Cost, Unrealized Gains And Losses, And Market Value of Investment Securities	The amortized cost, unrealized gains and losses, and market value of investment securities are shown as of December 31, 2017 and 2016 : Unrealized 2017 Cost Gains Losses Market Value Short-Term Investments: Certificate of Deposit $ 130,000,000 $ — $ — $ 130,000,000 Government Securities 9,024,777 — (13,647 ) 9,011,130 Mutual Funds 392,482 1,575 (476 ) 393,581 Corporate Bonds 12,952,229 — (7,230 ) 12,944,999 Other 188,344 — — 188,344 Long-Term Investments: Corporate Bonds 3,022,994 — (4,274 ) 3,018,720 Common Stocks 10,897,219 5,079,815 (273,663 ) 15,703,371 Mutual Funds 29,306,540 5,440,344 (65,547 ) 34,681,337 Preferred Stock 1,141,458 40,533 (3,000 ) 1,178,991 Total $ 196,926,043 $ 10,562,267 $ (367,837 ) $ 207,120,473 Unrealized 2016 Cost Gains Losses Market Value Short-Term Investments: Certificate of Deposit $ 130,000,000 $ — $ — $ 130,000,000 Government Securities 14,003,644 — (10,164 ) 13,993,480 Mutual Funds 26,326,674 27,459 (237,452 ) 26,116,681 Corporate Bonds 6,706,721 — (8,339 ) 6,698,382 Other 212,653 — — 212,653 Long-Term Investments: Corporate Bonds 1,955,292 — (6,736 ) 1,948,556 Common Stocks 9,825,550 3,349,962 (326,505 ) 12,849,007 Mutual Funds 27,329,164 1,830,992 (288,146 ) 28,872,010 Preferred Stock 745,462 360 (31,822 ) 714,000 Government Securities 5,519,668 661 (9,539 ) 5,510,790 Total $ 222,624,828 $ 5,209,434 $ (918,703 ) $ 226,915,559
Schedule of Unrealized Losses on Investments	Unrealized losses on investments as of December 31, 2017 are as follows: Aggregate Unrealized Losses Aggregate Fair Value Less than one year $ 263,655 $ 31,223,557 Greater than one year 104,182 285,077 Total $ 367,837 $ 31,508,634 Unrealized losses on investments as of December 31, 2016 are as follows: Aggregate Unrealized Losses Aggregate Fair Value Less than one year $ 767,612 $ 55,574,292 Greater than one year 151,091 358,120 Total $ 918,703 $ 55,932,412
Investments Classified by Contractual Maturity Date	Fixed income securities as of December 31, 2017 , have contractual maturities as follows: Due within one year $ 151,956,129 Due between one and five years 4,197,711 Due over five years — $ 156,153,840
Schedule of Inventories	Inventories consisted of the following as of December 31, 2017 and 2016 : 2017 2016 Raw materials $ 139,272,129 $ 115,099,569 Work-in-process 30,481,192 32,509,368 Finished goods 47,012,262 41,702,500 Total Inventory $ 216,765,583 $ 189,311,437
Schedule of Earnings Per Share Basic and Diluted	The following table reconciles the numerators and denominators used in the calculations of basic and diluted earnings per share (EPS) for each of the last three years: 2017 2016 2015 Numerators: Numerator for both basic and diluted EPS, net income $ 406,791,922 $ 347,591,276 $ 318,469,859 Denominators: Denominator for basic EPS, weighted-average common shares outstanding 285,864,997 288,433,772 293,096,212 Potentially dilutive shares resulting from stock option plans 2,361,092 2,638,544 3,141,687 Denominator for diluted EPS 288,226,089 291,072,316 296,237,899

Debt and Financing Arrangemen21

Debt and Financing Arrangements (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of notional amount of derivative financial instruments	The notional amount of the Company's derivative instruments are as follows: December 31, 2017 December 31, 2016 December 31, 2015 Interest Rate swap $ 150,000,000 $ 150,000,000 $ 150,000,000
Schedule of financial assets and liabilities measured at fair value in the consolidated balance sheets	The following table sets forth financial assets and liabilities measured at fair value in the consolidated balance sheets and the respective pricing levels to which the fair value measurements are classified within the fair value hierarchy. The Company uses the market approach to derive the value of its level 2 fair value measurements. Interest rate swaps are valued using publicized swap curves. Fair Value Measurements Quoted Prices with Other Observable Inputs (Level 2) December 31, 2017 December 31, 2016 December 31, 2015 Financial assets: Interest Rate Swap Asset $ — $ — $ — Financial Liabilities: Interest Rate Swap Liability (Other Accrued Liabilities) $ 230,845 $ 1,841,970 $ 2,947,438

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: 2017 2016 2015 Beginning of year $ 3,408,000 $ 5,375,000 $ 8,288,000 Additions based on tax positions related to the current year 941,000 756,000 1,765,000 Additions for tax positions in prior years 289,000 487,000 428,000 Reductions for tax positions in prior years (63,000 ) (2,949,000 ) (336,000 ) Reductions as a result of completed audit examinations — — (4,162,000 ) Reductions as a result of a lapse of the applicable statute of limitations (140,000 ) (261,000 ) (608,000 ) End of year $ 4,435,000 $ 3,408,000 $ 5,375,000
Schedule of Components of Provision For Income Taxes	The components of the provision for income taxes are as follows: 2017 2016 2015 Currently payable: Federal $ 133,166,194 $ 136,124,497 $ 129,379,597 State 3,984,000 3,805,000 2,908,000 Foreign 2,440,000 540,000 276,000 Total 139,590,194 140,469,497 132,563,597 Deferred income tax (benefit) expense: Primarily federal (14,585,412 ) 22,500,000 12,558,000 Provision for income taxes $ 125,004,782 $ 162,969,497 $ 145,121,597
Schedule of Effective Income Tax Rates Different From Statutory Federal Income Tax Rates	The effective income tax rates are different from the statutory federal income tax rates for the following reasons: 2017 2016 2015 Statutory federal income tax rate 35.00 % 35.00 % 35.00 % State income taxes, net of federal income tax benefit 0.50 0.50 0.40 Domestic production exclusion (2.80 ) (2.70 ) (2.80 ) Research tax credit (0.80 ) (0.80 ) (0.80 ) Increase (Reduction) in Reserve for Uncertain Tax Provisions 0.10 (0.20 ) (0.60 ) Change in Tax Rate on Deferred Taxes (7.20 ) — — Foreign Tax Credit (0.80 ) — — Other (0.50 ) 0.10 0.10 Effective income tax rate 23.50 % 31.90 % 31.30 %
Schedule of Deferred Income Tax Assets And Liabilities	The tax effect of temporary differences which give rise to deferred income tax assets and liabilities at December 31, 2017 and 2016 , are as follows: December 31, 2017 2016 Assets: Accruals not currently deductible $ 4,546,767 $ 4,282,470 Stock based compensation 8,594,640 18,701,361 Other 3,679,680 3,924,945 Total deferred income tax assets 16,821,087 26,908,776 Liabilities: Excess tax over book depreciation (46,123,681 ) (65,642,206 ) Goodwill (18,972,334 ) (23,225,969 ) Unrealized gain on investments (2,093,105 ) (1,435,322 ) Intangible assets (4,172,726 ) (5,368,886 ) Other (4,347,885 ) (2,449,012 ) Net deferred income taxes $ (58,888,644 ) $ (71,212,619 ) Net current and non-current tax assets and liabilities are included in the consolidated balance sheets as follows: December 31, 2017 2016 Long-term assets 16,821,087 26,908,776 Long-term liabilities (75,709,731 ) (98,121,395 ) Total deferred tax liability $ (58,888,644 ) $ (71,212,619 )

Stock-Based Compensation Plans

Stock-Based Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Weighted-Average Assumptions	The fair value of each option grant in the Non-employee Director Stock Option Plans was estimated on the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions for the indicated periods: 2017 2016 2015 Dividend yield (1) 2.2 % 2.2 % 2.1 % Expected volatility (2) 28.3 % 34.1 % 36.3 % Risk-free interest rate (3) 2.2 % 1.9 % 2.2 % Expected term of options (in years) (4) 6.4 6.2 6.0 Weighted-average grant-date fair value $ 5 $ 4 $ 5 (1) Represents the Company's estimated cash dividend yield over the expected term of option grant. (2) Amount is determined based on analysis of historical price volatility of the Company's common stock. The expected volatility is based on the daily percentage change in the price of the stock over a period equal to the expected term of the option grant. (3) Represents the U.S. Treasury yield over the expected term of the option grant. (4) Represents the period of time that options granted are expected to be outstanding. Based on analysis of historical option exercise activity, the Company has determined that non-employee directors exhibit similar exercise and post-vesting termination behavior. The fair value of each option grant in the Employee Stock Option Plan was estimated on the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions for the indicated periods: 2017 2016 2015 Dividend yield (1) 2.1 % 2.2 % 2.1 % Expected volatility (2) 26.7 % 33.2 % 35.8 % Risk-free interest rate (3) 2.0 % 1.4 % 1.5 % Expected term of options (in years) (4) 4.2 4.7 4.3 Weighted-average grant-date fair value $ 4 $ 4 $ 4 (1) Represents the Company's estimated cash dividend yield over the expected term of option grant. (2) Amount is determined based on analysis of historical price volatility of the Company's common stock. The expected volatility is based on the daily percentage change in the price of the stock over a period equal to the expected term of the option grant. (3) Represents the U.S. Treasury yield over the expected term of the option grant. (4) Represents the period of time that options granted are expected to be outstanding. Based on analysis of historical option exercise activity, the Company has determined that all employee groups exhibit similar exercise and post-vesting termination behavior.
Summary of Stock Option Activity	A summary of the status of the Company’s employee stock option plan at December 31, 2017 , 2016 and 2015 , and changes during the same periods are presented in the tables and narrative below. 2017 Shares (000) Wtd. Avg. Ex. Price Wtd. Avg. Remaining Contract Life Aggregate Intrinsic Value (000) Outstanding at Beginning of Year 14,252 $ 15 Granted 1,295 20 Exercised (3,476 ) 13 $ 25,156 Forfeited (234 ) 16 Outstanding at End of Year 11,837 16 2.7 Yrs $ 58,202 Exercisable at End of Year 5,297 $ 15 2 Yrs $ 32,152 2016 Shares (000) Wtd. Avg. Ex. Price Wtd. Avg. Remaining Contract Life Aggregate Intrinsic Value (000) Outstanding at Beginning of Year 17,692 $ 14 Granted 3,227 17 Exercised (6,291 ) 12 $ 31,790 Forfeited (376 ) 15 Outstanding at End of Year 14,252 15 3 Yrs $ 67,763 Exercisable at End of Year 4,855 $ 14 2.3 Yrs $ 30,021 2015 Shares (000) Wtd. Avg. Ex. Price Wtd. Avg. Remaining Contract Life Aggregate Intrinsic Value (000) Outstanding at Beginning of Year 17,829 $ 13 Granted 2,966 17 Exercised (2,344 ) 12 $ 11,596 Forfeited (759 ) 14 Outstanding at End of Year 17,692 14 3 Yrs $ 45,842 Exercisable at End of Year 6,858 $ 13 2.1 Yrs $ 23,917 A summary of the status of the Company’s Non-employee Director Stock Option Plan at December 31, 2017 , 2016 , and 2015 , and changes during the same periods are presented in the tables and narrative below: 2017 Shares (000) Wtd. Avg. Ex. Price Wtd. Avg. Remaining Contract Life Aggregate Intrinsic Value (000) Outstanding at Beginning of Year 381 $ 14 Granted 56 19 Exercised (31 ) 14 Forfeited — — Outstanding at End of Year 406 15 6.1 Yrs $ 2,565 Exercisable at End of Year 406 $ 15 6.1 Yrs $ 2,565 2016 Shares (000) Wtd. Avg. Ex. Price Wtd. Avg. Remaining Contract Life Aggregate Intrinsic Value (000) Outstanding at Beginning of Year 373 $ 13 Granted 56 16 Exercised (36 ) 10 Forfeited (12 ) 16 Outstanding at End of Year 381 14 6.4 Yrs $ 2,180 Exercisable at End of Year 381 $ 14 6.4 Yrs $ 2,180 2015 Shares (000) Wtd. Avg. Ex. Price Wtd. Avg. Remaining Contract Life Aggregate Intrinsic Value (000) Outstanding at Beginning of Year 381 $ 12 Granted 49 17 Exercised (57 ) 11 Forfeited — — Outstanding at End of Year 373 13 6.4 Yrs $ 1,069 Exercisable at End of Year 373 $ 13 6.4 Yrs $ 1,069
Schedule of Non-Vested Stock Option Activity	A summary of the status of the Company’s non-vested employee stock option activity for the years ended December 31, 2017 , 2016 , and 2015 , are presented in the table and narrative below: 2017 2016 2015 Shares (000) Wtd. Avg Grant Date Fair Value Shares (000) Wtd. Avg Grant Date Fair Value Shares (000) Wtd. Avg Grant Date Fair Value Nonvested Stock Options at Beginning of Year 9,397 $ 4 10,835 $ 4 13,265 $ 4 Granted 1,295 4 3,227 4 2,966 4 Vested (3,941 ) 4 (4,343 ) 4 (4,678 ) 4 Forfeited (211 ) 4 (322 ) 4 (718 ) 4 Nonvested Stock Options at End of Year 6,540 $ 4 9,397 $ 4 10,835 $ 4 A summary of the status of the Company’s nonvested Non-employee Director Stock Option Plan activity for the years ended December 31, 2017 , 2016 , and 2015 , are presented in the table and narrative below: 2017 2016 2015 Shares (000) Wtd. Avg Grant Date Fair Value Shares (000) Wtd. Avg Grant Date Fair Value Shares (000) Wtd. Avg Grant Date Fair Value Nonvested Stock Options at Beginning of Year — $ — — $ — — $ — Granted 56 5 56 4 49 5 Vested (56 ) 5 (56 ) 4 (49 ) 5 Forfeited — — — — — — Nonvested stock options at End of Year — $ — — $ — — $ —
Schedule of Employee Stock Purchase Plan	The following table summarizes shares sold to employees under the 2013 Plan in the years ended December 31, 2017 , 2016 and 2015 . Plan 2017 2016 2015 Cumulative Shares Issued in 2017 Weighted Average Fair Value 2017 2013 Employee Stock Purchase Plan 175,479 177,781 201,785 794,997 $ 17.12

Segment Reporting (Tables)

Segment Reporting (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Schedule of Automotive and Other Segment Reporting	2017 2016 2015 Revenue: Automotive Products United States $ 567,492,812 $ 554,945,912 $ 494,876,354 Germany 351,123,204 328,208,190 295,044,988 Japan 185,261,067 154,005,299 148,632,237 Other Countries 654,250,385 602,532,841 568,318,425 Other 36,745,110 39,232,514 36,745,702 Total $ 1,794,872,578 $ 1,678,924,756 $ 1,543,617,706 Income (Loss) from Operations: Automotive Products $ 512,895,699 $ 497,753,966 $ 445,067,511 Other 10,462,653 13,988,969 13,698,928 Total $ 523,358,352 $ 511,742,935 $ 458,766,439 Assets: Automotive Products $ 1,472,061,650 $ 1,457,989,335 $ 1,414,426,679 Other 9,576,514 9,384,154 9,429,994 Corporate 870,415,748 842,246,344 724,816,255 Total $ 2,352,053,912 $ 2,309,619,833 $ 2,148,672,928 Depreciation & Amortization: Automotive Products $ 95,378,100 $ 86,567,248 $ 78,925,332 Other 300,935 290,296 306,908 Corporate 3,891,873 1,729,886 1,366,927 Total $ 99,570,908 $ 88,587,430 $ 80,599,167 Capital Expenditures: Automotive Products $ 82,703,576 $ 99,811,083 $ 97,632,519 Other 170,357 200,262 161,247 Corporate 21,166,986 20,944,269 147,996 Total $ 104,040,919 $ 120,955,614 $ 97,941,762
Schedule of Major Product Line Revenues	Major product line revenues included within these segments are as follows: 2017 2016 2015 Automotive Products Automotive Mirrors $ 1,573,222,820 $ 1,456,963,758 $ 1,332,791,398 HomeLink ® Modules* 184,904,648 182,728,485 174,080,606 Total Automotive Products $ 1,758,127,468 $ 1,639,692,243 $ 1,506,872,004 Other Products Revenue $ 36,745,110 $ 39,232,513 $ 36,745,702 Total Revenue $ 1,794,872,578 $ 1,678,924,756 $ 1,543,617,706 *Excludes HomeLink ® revenue integrated into automotive mirrors.
Schedule of Automotive Customers Individually Accounted For 10% or More of Net Sales	In 2017 , the Company had four automotive customers (including direct sales to OEM customers and sales through their Tier 1 suppliers), which individually accounted for 10% or more of net sales as follows: Toyota Motor Corporation Volkswagen Group Ford Motor Company Daimler AG 2017 12 % 15 % 10 % 10 % 2016 11 % 14 % 11 % # 2015 11 % 14 % 11 % # # - Less than 10 percent.

Quarterly Financial Informati25

Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	The following table sets forth selected financial information for all of the quarters during the years ended December 31, 2017 and 2016 (in thousands, except per share data): First Second Third Fourth 2017 2016 2017 2016 2017 2016 2017 2016 Net Sales $ 453,535 $ 405,568 $ 443,139 $ 423,801 $ 438,628 $ 429,643 $ 459,570 $ 419,913 Gross Profit 175,801 158,691 167,208 166,773 171,230 173,822 180,290 169,167 Operating Income 134,427 120,849 125,865 128,746 129,073 134,212 133,994 127,936 Net Income 97,557 80,280 88,536 86,485 90,230 92,065 130,469 88,761 Earnings Per Share (Basic) $ 0.34 $ 0.28 $ 0.31 $ 0.30 $ 0.32 $ 0.32 $ 0.46 $ 0.31 Earnings Per Share (Diluted) $ 0.33 $ 0.28 $ 0.31 $ 0.30 $ 0.31 $ 0.32 $ 0.46 $ 0.31

Comprehensive Income (Tables)

Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2017
Comprehensive Income [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	Comprehensive income reflects the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. For the Company, comprehensive income represents net income adjusted for unrealized gains and losses on certain investments, foreign currency translation adjustments, and unrealized movement in derivative financial instruments designated as hedges. For the Twelve Months ended December 31, 2017 2016 2015 Foreign currency translation adjustments: Balance at beginning of period $ (2,862,999 ) $ (44,909 ) $ 1,403,899 Other comprehensive loss before reclassifications 3,508,029 (2,818,090 ) (1,448,808 ) Net current-period change 3,508,029 (2,818,090 ) (1,448,808 ) Balance at end of period 645,030 (2,862,999 ) (44,909 ) Unrealized gains (losses) on available-for-sale securities: Balance at beginning of period 2,788,975 829,907 10,868,322 Other comprehensive income (loss) before reclassifications 4,444,360 2,167,196 (5,513,842 ) Amounts reclassified from accumulated other comprehensive income (606,956 ) (208,128 ) (4,524,573 ) Net current-period change 3,837,404 1,959,068 (10,038,415 ) Balance at end of period 6,626,379 2,788,975 829,907 Unrealized gains (losses) on derivatives: Balance at beginning of period (1,197,281 ) (1,915,834 ) (959,206 ) Other comprehensive income (loss) before reclassifications 248,042 (672,419 ) (1,659,115 ) Amounts reclassified from accumulated other comprehensive income 871,213 1,390,972 702,487 Net current-period change 1,119,255 718,553 (956,628 ) Balance at end of period (78,026 ) (1,197,281 ) (1,915,834 ) Accumulated other comprehensive income (loss), end of period $ 7,193,383 $ (1,271,305 ) $ (1,130,836 ) All amounts are shown net of tax. Amounts in parentheses indicate debits.
Reclassification out of Accumulated Other Comprehensive Income	The following table presents details of reclassifications out of other comprehensive income for the twelve months ended December 31, 2017 , 2016 and 2015 . Details about Accumulated Other Comprehensive Income Components Affected Line item in the Statement of Consolidated Income For the Twelve Months ended December 31, 2017 2016 2015 Unrealized gains and (losses) on available-for-sale securities Realized gain on sale of securities $ 933,778 $ 320,197 $ 6,960,881 Other, net Provision for Income Taxes (326,822 ) (112,069 ) (2,436,308 ) Provision for Income Taxes Total reclassifications for the period $ 606,956 $ 208,128 $ 4,524,573 Net of tax Unrealized gains (losses) on derivatives Realized loss on interest rate swap $ (1,340,329 ) $ (2,139,958 ) $ (1,080,750 ) Other, net Provision for Income Taxes 469,116 748,986 378,263 Provision for Income Taxes $ (871,213 ) $ (1,390,972 ) $ (702,487 ) Net of tax Total reclassifications for the period $ (264,257 ) $ (1,182,844 ) $ 3,822,086 Net of tax

Goodwill and Other Intangible27

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	The carrying value of Goodwill as of December 31, 2017 and December 31, 2016 was $307.4 million as set forth in the table below. Carrying Amount Balance as of December 31, 2016 $ 307,365,845 Acquisitions — Divestitures — Impairments — Other — Balance as of December 31, 2017 $ 307,365,845
Schedule of Intangible Assets	The Intangible Assets and related change in carrying values are set forth in the table below as of December 31, 2017 and December 31, 2016 . As of December 31, 2017 : Other Intangible Assets Gross Accumulated Amortization Net Assumed Useful Life HomeLink ® Trade Names and Trademarks $ 52,000,000 $ — $ 52,000,000 Indefinite HomeLink ® Technology 180,000,000 (63,750,000 ) $ 116,250,000 12 years Existing Customer Platforms 43,000,000 (18,275,000 ) $ 24,725,000 10 years Exclusive Licensing Agreement 96,000,000 — $ 96,000,000 Indefinite Total other identifiable intangible assets 371,000,000 (82,025,000 ) 288,975,000 As of December 31, 2016 : Other Intangible Assets Gross Accumulated Amortization Net Assumed Useful Life HomeLink ® Trade Names and Trademarks $ 52,000,000 $ — $ 52,000,000 Indefinite HomeLink ® Technology 180,000,000 (48,750,000 ) $ 131,250,000 12 years Existing Customer Platforms 43,000,000 (13,975,000 ) $ 29,025,000 10 years Exclusive Licensing Agreement 96,000,000 — $ 96,000,000 Indefinite Total other identifiable intangible assets 371,000,000 (62,725,000 ) 308,275,000

Summary of Significant Accoun28

Summary of Significant Accounting and Reporting Policies (Narrative) (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)plan$ / sharesshares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)shares
Summary Of Significant Accounting And Reporting Policies [Line Items]
Equity Investment losses were considered to be other than temporary		$ 0	$ 0
Allowance for obsolete and slow moving inventories		$ 6,600,000	6,100,000
Allowance for obsolete and slow moving inventories, percent		3.00%
Depreciation expense		$ 77,000,000	66,300,000	$ 58,100,000
Advertising and promotional costs		2,600,000	1,900,000	1,400,000
Repair and maintenance of plant and equipment		$ 24,600,000	$ 22,100,000	$ 20,700,000
Shares related to stock plans not included in diluted average common shares outstanding because their effect would be antidilutive | shares		910,105	1,985,849	1,656,936
Loss on ineffectiveness of hedge		$ 100,000	$ 0
Net discrete tax benefit		5,200,000
Net tax benefits recognized as additional paid-in capital			3,200,000	$ 1,200,000
Tax benefits associated with the exercise, vesting or disposition of stock under stock plans recognized as an adjustment of additional paid-in capital		8,300,000	11,800,000	5,000,000
Net cash (used for) financing activities		400,032,789	230,682,529	210,550,768
Net cash flows from operating activities		$ 501,002,780	477,048,185	354,416,152
Accounting Standards Update 2016-09 [Member]
Summary Of Significant Accounting And Reporting Policies [Line Items]
Effect of change on earnings per share (in dollars per share) | $ / shares		$ 0.02
Net cash (used for) financing activities			5,600,000
Net cash flows from operating activities			5,600,000
Accounting Standards Update 2016-01 [Member] | Scenario, Forecast [Member]
Summary Of Significant Accounting And Reporting Policies [Line Items]
Cumulative-effect adjustment	$ 7,000,000
Buildings and improvements | Minimum
Summary Of Significant Accounting And Reporting Policies [Line Items]
Minimum estimated useful life, in years		7 years
Buildings and improvements | Maximum
Summary Of Significant Accounting And Reporting Policies [Line Items]
Minimum estimated useful life, in years		30 years
Machinery and equipment | Minimum
Summary Of Significant Accounting And Reporting Policies [Line Items]
Minimum estimated useful life, in years		3 years
Machinery and equipment | Maximum
Summary Of Significant Accounting And Reporting Policies [Line Items]
Minimum estimated useful life, in years		10 years
Employee Stock Option [Member]
Summary Of Significant Accounting And Reporting Policies [Line Items]
Number of plans | plan		2
Additional Paid-In Capital
Summary Of Significant Accounting And Reporting Policies [Line Items]
Net tax benefits recognized as additional paid-in capital			3,200,000	1,200,000
Tax benefits associated with the exercise, vesting or disposition of stock under stock plans recognized as an adjustment of additional paid-in capital			4,900,000	1,700,000
Tax expense associated with the exercise, vesting or disposition of stock under stock plans recognized as an adjustment of additional paid-in capital			$ 1,700,000	$ 500,000

Summary of Significant Accoun29

Summary of Significant Accounting and Reporting Policies (Schedule Of Allowance For Doubtful Accounts) (Details) - Allowance for Doubtful Accounts - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Activity in the Company’s allowance for doubtful accounts
Beginning Balance	$ 2,917,424	$ 2,663,477	$ 2,711,248
Net Additions/ (Reductions) to Costs and Expenses	0	0	0
Deductions and Other Adjustments	(202,891)	253,947	(47,771)
Ending Balance	$ 2,714,533	$ 2,917,424	$ 2,663,477

Summary of Significant Accoun30

Summary of Significant Accounting and Reporting Policies (Schedule of Assets or Liabilities Having Recurring Measurements) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash & Cash Equivalents	$ 569,734,496	$ 546,477,075
Total	776,854,969	773,392,634
Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	130,000,000	130,000,000
Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	9,011,130	13,993,480
Long-Term Investments		5,510,790
Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	12,944,999	6,698,382
Long-Term Investments	3,018,720	1,948,556
Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	188,344	212,653
Common Stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-Term Investments	15,703,371	12,849,007
Mutual Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	393,581	26,116,681
Long-Term Investments	34,681,337	28,872,010
Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-Term Investments	1,178,991	714,000
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash & Cash Equivalents	569,734,496	546,477,075
Total	751,486,539	719,124,745
Level 1 | Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	130,000,000	130,000,000
Level 1 | Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	0	0
Long-Term Investments		0
Level 1 | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	0	0
Long-Term Investments	0	0
Level 1 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	188,344	212,653
Level 1 | Common Stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-Term Investments	15,703,371	12,849,007
Level 1 | Mutual Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	0	0
Long-Term Investments	34,681,337	28,872,010
Level 1 | Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-Term Investments	1,178,991	714,000
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash & Cash Equivalents	0	0
Total	25,368,430	54,267,889
Level 2 | Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	0	0
Level 2 | Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	9,011,130	13,993,480
Long-Term Investments		5,510,790
Level 2 | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	12,944,999	6,698,382
Long-Term Investments	3,018,720	1,948,556
Level 2 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	0	0
Level 2 | Common Stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-Term Investments	0	0
Level 2 | Mutual Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	393,581	26,116,681
Long-Term Investments	0	0
Level 2 | Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-Term Investments	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash & Cash Equivalents	0	0
Level 3 | Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	0	0
Level 3 | Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	0	0
Long-Term Investments		0
Level 3 | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	0	0
Long-Term Investments	0	0
Level 3 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	0	0
Level 3 | Common Stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-Term Investments	0	0
Level 3 | Mutual Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-Term Investments	0	0
Long-Term Investments	0	0
Level 3 | Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-Term Investments	$ 0	$ 0

Summary of Significant Accoun31

Summary of Significant Accounting and Reporting Policies (Schedule of Amortized Cost, Unrealized Gains And Losses, And Market Value Of Investment Securities) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 196,926,043	$ 222,624,828
Unrealized Gains	10,562,267	5,209,434
Unrealized Losses	(367,837)	(918,703)
Market Value	207,120,473	226,915,559
Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Cost	130,000,000	130,000,000
Unrealized Gains	0	0
Unrealized Losses	0	0
Market Value	130,000,000	130,000,000
Government Securities
Schedule of Available-for-sale Securities [Line Items]
Cost	9,024,777	14,003,644
Unrealized Gains	0	0
Unrealized Losses	(13,647)	(10,164)
Market Value	9,011,130	13,993,480
Mutual Funds
Schedule of Available-for-sale Securities [Line Items]
Cost	392,482	26,326,674
Unrealized Gains	1,575	27,459
Unrealized Losses	(476)	(237,452)
Market Value	393,581	26,116,681
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Cost	12,952,229	6,706,721
Unrealized Gains	0	0
Unrealized Losses	(7,230)	(8,339)
Market Value	12,944,999	6,698,382
Other
Schedule of Available-for-sale Securities [Line Items]
Cost	188,344	212,653
Unrealized Gains	0	0
Unrealized Losses	0	0
Market Value	188,344	212,653
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Cost	3,022,994	1,955,292
Unrealized Gains	0	0
Unrealized Losses	(4,274)	(6,736)
Market Value	3,018,720	1,948,556
Common Stocks
Schedule of Available-for-sale Securities [Line Items]
Cost	10,897,219	9,825,550
Unrealized Gains	5,079,815	3,349,962
Unrealized Losses	(273,663)	(326,505)
Market Value	15,703,371	12,849,007
Mutual Funds – Equity
Schedule of Available-for-sale Securities [Line Items]
Cost	29,306,540	27,329,164
Unrealized Gains	5,440,344	1,830,992
Unrealized Losses	(65,547)	(288,146)
Market Value	34,681,337	28,872,010
Preferred Stock
Schedule of Available-for-sale Securities [Line Items]
Cost	1,141,458	745,462
Unrealized Gains	40,533	360
Unrealized Losses	(3,000)	(31,822)
Market Value	$ 1,178,991	714,000
Government Securities
Schedule of Available-for-sale Securities [Line Items]
Cost		5,519,668
Unrealized Gains		661
Unrealized Losses		(9,539)
Market Value		$ 5,510,790

Summary of Significant Accoun32

Summary of Significant Accounting and Reporting Policies (Schedule of Unrealized Losses on Investments) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Aggregate Unrealized Losses, Less than one year	$ 263,655	$ 767,612
Aggregate Fair Value, Less than one year	31,223,557	55,574,292
Aggregate Unrealized Losses, Greater than one year	104,182	151,091
Aggregate Fair Value, Greater than one year	285,077	358,120
Aggregate Unrealized Losses, Total	367,837	918,703
Aggregate Fair Value, Total	$ 31,508,634	$ 55,932,412

Summary of Significant Accoun33

Summary of Significant Accounting and Reporting Policies (Fixed Income Securities Contractual Maturity) (Details) - Fixed Income Securities [Member]	Dec. 31, 2017USD ($)
Schedule of Available-for-sale Securities [Line Items]
Due within one year	$ 151,956,129
Due between one and five years	4,197,711
Due over five years	0
Total	$ 156,153,840

Summary of Significant Accoun34

Summary of Significant Accounting and Reporting Policies (Inventories) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Raw materials	$ 139,272,129	$ 115,099,569
Work-in-process	30,481,192	32,509,368
Finished goods	47,012,262	41,702,500
Total Inventory	$ 216,765,583	$ 189,311,437

Summary of Significant Accoun35

Summary of Significant Accounting and Reporting Policies (Schedule of Earnings Per Share, Basic And Diluted) (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
Numerators:
Numerator for both basic and diluted EPS, net income	$ 130,469,000	$ 90,230,000	$ 88,536,000	$ 97,557,000	$ 88,761,000	$ 92,065,000	$ 86,485,000	$ 80,280,000	$ 406,791,922	$ 347,591,276	$ 318,469,859
Denominators:
Denominator for basic EPS, weighted-average common shares outstanding (in shares)									285,864,997	288,433,772	293,096,212
Potentially dilutive shares resulting from stock option plans (in shares)									2,361,092	2,638,544	3,141,687
Denominator for diluted EPS (in shares)									288,226,089	291,072,316	296,237,899

Debt and Financing Arrangemen36

Debt and Financing Arrangements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jul. 31, 2015	Oct. 01, 2014	Sep. 27, 2013
Debt Instrument [Line Items]
Amount outstanding	$ 0	$ 178,125,000
Financial Liabilities:
Effect of 1% increase on borrowing rate to interest expense (less than $0.1 million)	100,000			$ 100,000
Interest Rate Swap
Debt Instrument [Line Items]
Amount of hedged item					$ 150,000,000
Interest rate of derivative					1.89%
Notional amount of derivative liability	150,000,000	150,000,000	$ 150,000,000		$ 150,000,000
Derivative expense	1,300,000	2,100,000
Interest Rate Swap | Level 2
Financial assets:
Interest Rate Swap Asset	0	0	0
Financial Liabilities:
Interest Rate Swap Liability (Other Accrued Liabilities)	230,845	1,841,970	$ 2,947,438
Other, net
Debt Instrument [Line Items]
Payments of financing charges	$ 3,000,000	3,500,000
LIBOR Rate
Debt Instrument [Line Items]
Basis spread on variable rate	2.57%
Term Loan and Revolving Facility
Debt Instrument [Line Items]
Extinguishment of debt amount	$ 107,600,000	$ 47,500,000
Term Loan
Debt Instrument [Line Items]
Extinguishment of debt amount	100,000,000
Revolving Facility
Debt Instrument [Line Items]
Extinguishment of debt amount	40,000,000
Credit Agreement
Debt Instrument [Line Items]
Additional principal amount available (up to)						$ 75,000,000
Revolving Facility
Debt Instrument [Line Items]
Principal amount						150,000,000
Amount outstanding	0
Available borrowing capacity	149,300,000
Term Loan
Debt Instrument [Line Items]
Principal amount						150,000,000
Amount outstanding	$ 78,000,000
Swing Loans
Debt Instrument [Line Items]
Additional principal amount available (up to)						20,000,000
Letters of Credit
Debt Instrument [Line Items]
Additional principal amount available (up to)						$ 20,000,000

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Reduction of net deferred tax liability	$ 38,400
Tax benefits associated with the exercise, vesting or disposition of stock under stock plans recognized as an adjustment of additional paid-in capital		$ 8,300	$ 11,800	$ 5,000
Income taxes paid		126,000	144,100	$ 138,000
Provisional estimate for transition tax		1,200
Unrecognized tax benefits accrued interest	$ 433	$ 433	$ 277

Income Taxes (Schedule Of Compo

Income Taxes (Schedule Of Components Of Provision For Income Taxes) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Currently payable:
Federal	$ 133,166,194	$ 136,124,497	$ 129,379,597
State	3,984,000	3,805,000	2,908,000
Foreign	2,440,000	540,000	276,000
Total	139,590,194	140,469,497	132,563,597
Deferred income tax (benefit) expense:
Primarily federal	(14,585,412)	22,500,000	12,558,000
Provision for income taxes	$ 125,004,782	$ 162,969,497	$ 145,121,597

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rates Different From Statutory Federal Income Tax Rates) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Statutory federal income tax rate	35.00%	35.00%	35.00%
State income taxes, net of federal income tax benefit	0.50%	0.50%	0.40%
Domestic production exclusion	(2.80%)	(2.70%)	(2.80%)
Research tax credit	(0.80%)	(0.80%)	(0.80%)
Increase (Reduction) in Reserve for Uncertain Tax Provisions	0.10%	(0.20%)	(0.60%)
Change in Tax Rate on Deferred Taxes	(7.20%)	0.00%	0.00%
Foreign Tax Credit	(0.80%)	(0.00%)	(0.00%)
Other	(0.50%)	0.10%	0.10%
Effective income tax rate	23.50%	31.90%	31.30%

Income Taxes (Schedule Of Defer

Income Taxes (Schedule Of Deferred Income Tax Assets And Liabilities) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Assets:
Accruals not currently deductible	$ 4,546,767	$ 4,282,470
Stock based compensation	8,594,640	18,701,361
Other	3,679,680	3,924,945
Total deferred income tax assets	16,821,087	26,908,776
Liabilities:
Excess tax over book depreciation	(46,123,681)	(65,642,206)
Goodwill	(18,972,334)	(23,225,969)
Unrealized gain on investments	(2,093,105)	(1,435,322)
Intangible assets	(4,172,726)	(5,368,886)
Other	(4,347,885)	(2,449,012)
Net deferred income taxes	$ (58,888,644)	$ (71,212,620)

Income Taxes (Schedule of Def41

Income Taxes (Schedule of Deferred Tax Liabiliites) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Long-term assets	$ 16,821,087	$ 26,908,776
Long-term liabilities	(75,709,731)	(98,121,395)
Deferred Tax Liabilities, Net	$ 58,888,644	$ 71,212,620

Income Taxes (Schedule Of Recon

Income Taxes (Schedule Of Reconciliation Of Beginning And Ending Amount Of Unrecognized Tax Benefits ) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of the beginning and ending amount of unrecognized tax benefits
Beginning of year	$ 3,408,000	$ 5,375,000	$ 8,288,000
Additions based on tax positions related to the current year	941,000	756,000	1,765,000
Additions for tax positions in prior years	289,000	487,000	428,000
Reductions for tax positions in prior years	(63,000)	(2,949,000)	(336,000)
Reductions as a result of completed audit examinations	0	0	(4,162,000)
Reductions as a result of a lapse of the applicable statute of limitations	(140,000)	(261,000)	(608,000)
End of year	$ 4,435,000	$ 3,408,000	$ 5,375,000

Employee Benefit Plan (Details)

Employee Benefit Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Company's contributions under 401(k) retirement savings plan	$ 7.7	$ 6.5	$ 5.7

Stock-Based Compensation Plan44

Stock-Based Compensation Plans (Narrative) (Details)	12 Months Ended
	Dec. 31, 2017USD ($)plan$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares	May 31, 2014shares	Dec. 31, 2013shares	Dec. 31, 2012shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost | $	$ 0
Employee Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options available for grant (in shares)				24,000,000
Options granted net of shares from canceled/expired options (in shares)	11,404,018
Unrecognized compensation cost | $	$ 9,957,103
Weighted-average period for unrecognized compensation cost expected to be recognized	1 year 9 months
Non-Employee Director Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option vesting period	6 months
Shares approved (in shares)						1,000,000
Grants in period (in shares)	1,074,480
Option expiration period, years	10 years
Previous Non-Employee Director Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)	427,000
Restricted Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares approved (in shares)			9,000,000
Restricted period, maximum, in years			10 years
Shares granted with restriction period (in shares)	2,019,404
Shares, granted (in shares)	5,334,225
Unearned stock-based compensation | $	$ 22,417,962
Amortization expense | $	$ 5,353,339	$ 3,885,042	$ 3,486,242
Restricted Stock Plan, Five Years [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted with restriction period (in shares)	228,630	246,660	229,660
Restricted period for granted shares, in years	5 years
Restricted Stock Plan, Four Years [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted with restriction period (in shares)	628,015
Restricted period for granted shares, in years	4 years
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares approved (in shares)					2,000,000
ESPP discount rate	85.00%
Discount recognized as compensation expense	15.00%
Employee Stock Purchase Plan, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares sold to employees during period (in shares)	175,479	177,781	201,785
Cumulative shares sold to employees during period (in shares)	794,997
Weighted average fair value of shares sold (in dollars per share) | $ / shares	$ 17.12
Minimum | Employee Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option vesting period	1 year
Award expiration period	5 years
Minimum | Restricted Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Market price (in dollars per share) | $ / shares	$ 18.97	$ 14.70	$ 15.50
Maximum | Employee Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option vesting period	5 years
Award expiration period	7 years
Maximum | Restricted Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Market price (in dollars per share) | $ / shares	$ 21.33	$ 19.69	$ 18.30
Stock Compensation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of plans | plan	4
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of plans | plan	2

Stock-Based Compensation Plan45

Stock-Based Compensation Plans (Schedule of Weighted-Average Assumptions) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	2.10%	2.20%	2.10%
Expected volatility	26.70%	33.20%	35.80%
Risk-free interest rate	2.00%	1.40%	1.50%
Expected term of options (in years)	4 years 2 months 12 days	4 years 8 months 12 days	4 years 3 months 18 days
Weighted-average grant-date fair value (in dollars per share)	$ 4	$ 4	$ 4
Non-Employee Director Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	2.20%	2.20%	2.10%
Expected volatility	28.30%	34.10%	36.30%
Risk-free interest rate	2.20%	1.90%	2.20%
Expected term of options (in years)	6 years 4 months 24 days	6 years 2 months 12 days	6 years
Weighted-average grant-date fair value (in dollars per share)	$ 5	$ 4	$ 5

Stock-Based Compensation Plan46

Stock-Based Compensation Plans (Summary of Stock Option Activity) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares, Outstanding at Beginning of Year (in shares)	14,252	17,692	17,829
Shares, Granted (in shares)	1,295	3,227	2,966
Shares, Exercised (in shares)	(3,476)	(6,291)	(2,344)
Shares, Forfeited (in shares)	(234)	(376)	(759)
Shares, Outstanding at End of Year (in shares)	11,837	14,252	17,692
Shares, Exercisable at End of Year (in shares)	5,297	4,855	6,858
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Wtd. Avg. Ex. Price, Outstanding at Beginning of Year (in dollars per share)	$ 15	$ 14	$ 13
Wtd. Avg. Ex. Price, Granted (in dollars per share)	20	17	17
Wtd. Avg. Ex. Price, Exercised (in dollars per share)	13	12	12
Wtd. Avg. Ex. Price, Forfeited (in dollars per share)	16	15	14
Wtd. Avg. Ex. Price, Outstanding at End of Year (in dollars per share)	16	15	14
Wtd. Avg. Ex. Price, Exercisable at End of Year (in dollars per share)	$ 15	$ 14	$ 13
Option expiration period, years	2 years 8 months 12 days	3 years	3 years
Wtd. Avg. Remaining Contract Life, Exercisable at End of Year	2 years	2 years 3 months 18 days	2 years 1 month 6 days
Aggregate Intrinsic Value, Exercised	$ 25,156	$ 31,790	$ 11,596
Aggregate Intrinsic Value, Outstanding at End of Year	58,202	67,763	45,842
Aggregate Intrinsic Value, Exercisable at End of Year	$ 32,152	$ 30,021	$ 23,917
Non-Employee Director Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares, Outstanding at Beginning of Year (in shares)	381	373	381
Shares, Granted (in shares)	56	56	49
Shares, Exercised (in shares)	(31)	(36)	(57)
Shares, Forfeited (in shares)	0	(12)	0
Shares, Outstanding at End of Year (in shares)	406	381	373
Shares, Exercisable at End of Year (in shares)	406	381	373
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Wtd. Avg. Ex. Price, Outstanding at Beginning of Year (in dollars per share)	$ 14	$ 13	$ 12
Wtd. Avg. Ex. Price, Granted (in dollars per share)	19	16	17
Wtd. Avg. Ex. Price, Exercised (in dollars per share)	14	10	11
Wtd. Avg. Ex. Price, Forfeited (in dollars per share)	0	16	0
Wtd. Avg. Ex. Price, Outstanding at End of Year (in dollars per share)	15	14	13
Wtd. Avg. Ex. Price, Exercisable at End of Year (in dollars per share)	$ 15	$ 14	$ 13
Option expiration period, years	6 years 1 month 6 days	6 years 4 months 24 days	6 years 4 months 24 days
Wtd. Avg. Remaining Contract Life, Exercisable at End of Year	6 years 1 month 6 days	6 years 4 months 24 days	6 years 4 months 24 days
Aggregate Intrinsic Value, Exercised
Aggregate Intrinsic Value, Outstanding at End of Year	2,565	2,180	1,069
Aggregate Intrinsic Value, Exercisable at End of Year	$ 2,565	$ 2,180	$ 1,069

Stock-Based Compensation Plan47

Stock-Based Compensation Plans (Schedule of Non-Vested Stock Option Activity) (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Shares, Nonvested stock options at Beginning of Year (in shares)	9,397	10,835	13,265
Shares, Granted (in shares)	1,295	3,227	2,966
Shares, Vested (in shares)	(3,941)	(4,343)	(4,678)
Shares, Forfeited (in shares)	(211)	(322)	(718)
Shares, Nonvested stock options at End of Year (in shares)	6,540	9,397	10,835
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Wtd. Avg Grant Date Fair Value, Nonvested stock options at Beginning of Year (in dollars per share)	$ 4	$ 4	$ 4
Wtd. Avg Grant Date Fair Value, Granted (in dollars per share)	4	4	4
Wtd. Avg Grant Date Fair Value, Vested (in dollars per share)	4	4	4
Wtd. Avg Grant Date Fair Value, Forfeited (in dollars per share)	4	4	4
Wtd. Avg Grant Date Fair Value, Nonvested stock options at End of Year (in dollars per share)	$ 4	$ 4	$ 4
Non-Employee Director Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Shares, Nonvested stock options at Beginning of Year (in shares)	0	0	0
Shares, Granted (in shares)	56	56	49
Shares, Vested (in shares)	(56)	(56)	(49)
Shares, Forfeited (in shares)	0	0	0
Shares, Nonvested stock options at End of Year (in shares)	0	0	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Wtd. Avg Grant Date Fair Value, Nonvested stock options at Beginning of Year (in dollars per share)	$ 0	$ 0	$ 0
Wtd. Avg Grant Date Fair Value, Granted (in dollars per share)	5	4	5
Wtd. Avg Grant Date Fair Value, Vested (in dollars per share)	5	4	5
Wtd. Avg Grant Date Fair Value, Forfeited (in dollars per share)	0	0	0
Wtd. Avg Grant Date Fair Value, Nonvested stock options at End of Year (in dollars per share)	$ 0	$ 0	$ 0

Segment Reporting (Schedule of

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

Segment Reporting (Schedule o49

Segment Reporting (Schedule of Major Product Line Revenues) (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
Revenue from External Customer [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
Automotive Products
Revenue from External Customer [Line Items]
Revenues									1,758,127,468	1,639,692,243	1,506,872,004
Automotive Products | Automotive Mirrors
Revenue from External Customer [Line Items]
Revenues									1,573,222,820	1,456,963,758	1,332,791,398
Automotive Products | HomeLink Modules
Revenue from External Customer [Line Items]
Revenues									184,904,648	182,728,485	174,080,606
Other | Other Products Revenue
Revenue from External Customer [Line Items]
Revenues									$ 36,745,110	$ 39,232,513	$ 36,745,702

Segment Reporting (Schedule o50

Segment Reporting (Schedule of Automotive Customers Individually Accounted For 10% or More of Net Sales) (Details) - automotive_customer	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue, Major Customer [Line Items]
Percentage net sales invoiced and paid in foreign currencies	8.00%	7.00%	6.00%
Number of customers which individually accounted for 10% or more of net sales	4
Customer concentration risk | Toyota Motor Corporation
Revenue, Major Customer [Line Items]
Percentage of revenue individually accounted by customers (less than 10% for Daimler AG in 2016 and 2015)	12.00%	11.00%	11.00%
Customer concentration risk | Volkswagen Group
Revenue, Major Customer [Line Items]
Percentage of revenue individually accounted by customers (less than 10% for Daimler AG in 2016 and 2015)	15.00%	14.00%	14.00%
Customer concentration risk | Ford Motor Company
Revenue, Major Customer [Line Items]
Percentage of revenue individually accounted by customers (less than 10% for Daimler AG in 2016 and 2015)	10.00%	11.00%	11.00%
Customer concentration risk | Daimler AG
Revenue, Major Customer [Line Items]
Percentage of revenue individually accounted by customers (less than 10% for Daimler AG in 2016 and 2015)	10.00%	10.00%	10.00%

Quarterly Financial Informati51

Quarterly Financial Information (Unaudited) (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
Quarterly Financial Information Disclosure [Abstract]
Net Sales	$ 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
Gross Profit	180,290,000	171,230,000	167,208,000	175,801,000	169,167,000	173,822,000	166,773,000	158,691,000	694,528,266	668,452,244	603,776,052
Operating Income	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
Net Income	$ 130,469,000	$ 90,230,000	$ 88,536,000	$ 97,557,000	$ 88,761,000	$ 92,065,000	$ 86,485,000	$ 80,280,000	$ 406,791,922	$ 347,591,276	$ 318,469,859
Earnings Per Share (Basic) (in dollars per share)	$ 0.46	$ 0.32	$ 0.31	$ 0.34	$ 0.31	$ 0.32	$ 0.30	$ 0.28	$ 1.42	$ 1.21	$ 1.09
Earnings Per Share (Diluted) (in dollars per share)	$ 0.46	$ 0.31	$ 0.31	$ 0.33	$ 0.31	$ 0.32	$ 0.30	$ 0.28	$ 1.41	$ 1.19	$ 1.08

Comprehensive Income (AOCI Roll

Comprehensive Income (AOCI Rollforward) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 1,910,424,234	$ 1,722,516,761	$ 1,571,412,445
Comprehensive Income	415,256,610	347,450,807	306,026,008
Ending balance	2,049,518,261	1,910,424,234	1,722,516,761
Accumulated other comprehensive income (loss), end of period	7,193,383	(1,271,305)	(1,130,836)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(2,862,999)	(44,909)	1,403,899
Other comprehensive income (loss) before reclassifications	3,508,029	(2,818,090)	(1,448,808)
Comprehensive Income	3,508,029	(2,818,090)	(1,448,808)
Ending balance	645,030	(2,862,999)	(44,909)
Unrealized gains(losses) on available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	2,788,975	829,907	10,868,322
Other comprehensive income (loss) before reclassifications	4,444,360	2,167,196	(5,513,842)
Amounts reclassified from accumulated other comprehensive income	(606,956)	(208,128)	(4,524,573)
Comprehensive Income	3,837,404	1,959,068	(10,038,415)
Ending balance	6,626,379	2,788,975	829,907
Unrealized gains (losses) on derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,197,281)	(1,915,834)	(959,206)
Other comprehensive income (loss) before reclassifications	248,042	(672,419)	(1,659,115)
Amounts reclassified from accumulated other comprehensive income	871,213	1,390,972	702,487
Comprehensive Income	1,119,255	718,553	(956,628)
Ending balance	$ (78,026)	$ (1,197,281)	$ (1,915,834)

Comprehensive Income (Reclassif

Comprehensive Income (Reclassification Out of Accumulated Other Comprehensive Income) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Provision for Income Taxes	$ (125,004,782)	$ (162,969,497)	$ (145,121,597)
Amounts Reclassified from Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	(264,257)	(1,182,844)	3,822,086
Amounts Reclassified from Other Comprehensive Income | Unrealized gains and (losses) on available-for-sale securities
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Realized gain (loss)	933,778	320,197	6,960,881
Provision for Income Taxes	(326,822)	(112,069)	(2,436,308)
Total reclassifications for the period	606,956	208,128	4,524,573
Amounts Reclassified from Other Comprehensive Income | Unrealized gains (losses) on derivatives
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Realized gain (loss)	(1,340,329)	(2,139,958)	(1,080,750)
Provision for Income Taxes	469,116	748,986	378,263
Total reclassifications for the period	$ (871,213)	$ (1,390,972)	$ (702,487)

Goodwill and Other Intangible54

Goodwill and Other Intangible Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2013
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Goodwill	$ 307,365,845	$ 307,365,845
Amortization expense	22,500,000	22,300,000	$ 22,500,000
Patents and Other Intangible Assets [Member]
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ 101,000,000	79,200,000
Finite-lived intangible asset, useful life	10 years
Amortization expense, 2018	$ 22,000,000
Amortization expense, 2019	22,000,000
Amortization expense, 2020	22,000,000
Amortization expense, 2021	22,000,000
Amortization expense, 2022	21,000,000
HomeLink®
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Goodwill				$ 307,400,000
Accumulated amortization	$ 82,025,000	$ 62,725,000

Goodwill and Other Intangible55

Goodwill and Other Intangible Assets (Schedule of Goodwill) (Details)	12 Months Ended
	Dec. 31, 2017USD ($)
Goodwill [Roll Forward]
Balance as of December 31, 2016	$ 307,365,845
Acquisitions	0
Divestitures	0
Impairments	0
Other	0
Balance as of December 31, 2017	$ 307,365,845

Goodwill and Other Intangible56

Goodwill and Other Intangible Assets (Schedule of Intangible Assets) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangible assets, net	$ 288,975,000	$ 308,275,000
HomeLink®
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, accumulated amortization	(82,025,000)	(62,725,000)
Intangible assets, gross	371,000,000	371,000,000
Intangible assets, net	288,975,000	308,275,000
HomeLink® | Homelink Technology
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	180,000,000	180,000,000
Finite-lived intangible assets, accumulated amortization	(63,750,000)	(48,750,000)
Finite-lived intangible assets, net	$ 116,250,000	$ 131,250,000
Finite-lived intangible asset, useful life	12 years	12 years
HomeLink® | Existing Customer Platforms
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 43,000,000	$ 43,000,000
Finite-lived intangible assets, accumulated amortization	(18,275,000)	(13,975,000)
Finite-lived intangible assets, net	$ 24,725,000	$ 29,025,000
Finite-lived intangible asset, useful life	10 years	10 years
HomeLink® | HomeLink Trade Names and Trademarks
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	$ 52,000,000	$ 52,000,000
HomeLink® | Exclusive Licensing Agreement
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	$ 96,000,000	$ 96,000,000