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