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Summary of Significant Accounting and Reporting Policies (Narrative) (Details) | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2018 USD ($) | Dec. 31, 2018 USD ($) plan shares | Dec. 31, 2017 USD ($) shares | Dec. 31, 2016 USD ($) shares | Sep. 30, 2018 USD ($)
Summary Of Significant Accounting And Reporting Policies [Line Items] |  |  |  |  |
Technology investments |  |  |  |  | $ 3,850,000
Technology investments percentage |  |  | 20.00% |  |
Equity Investment losses were considered to be other than temporary |  | $ 0 | $ 0 |  |
Allowance for obsolete and slow moving inventories |  | 7,800,000 | 6,600,000 |  |
Depreciation expense |  | 79,700,000 | 77,000,000.0 | $ 66,300,000 |
Advertising and promotional costs |  | 2,500,000 | 2,600,000 | 1,900,000 |
Repair and maintenance of plant and equipment |  | $ 28,900,000 | $ 24,600,000 | $ 22,100,000 |
Shares related to stock plans not included in diluted average common shares outstanding because their effect would be antidilutive | shares |  | 698,019 | 910,105 | 1,985,849 |
Net cash flows from operating activities |  | $ 552,418,646 | $ 501,002,780 | $ 477,048,185 |
Accounting Standards Update 2016-01 |  |  |  |  |
Summary Of Significant Accounting And Reporting Policies [Line Items] |  |  |  |  |
Cumulative-effect adjustment | $ 6,642,727 |  |  |  |
Minimum | Accounting Standards Update 2018-11 |  |  |  |  |
Summary Of Significant Accounting And Reporting Policies [Line Items] |  |  |  |  |
Expected right-of-use asset and right -of-use liability |  | 2,000,000 |  |  |
Maximum | Accounting Standards Update 2018-11 |  |  |  |  |
Summary Of Significant Accounting And Reporting Policies [Line Items] |  |  |  |  |
Expected right-of-use asset and right -of-use liability |  | $ 3,000,000 |  |  |
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 |  |  |  |  |
Summary Of Significant Accounting And Reporting Policies [Line Items] |  |  |  |  |
Number of plans | plan |  | 2 |  |  |

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