Summary of Significant Accounting and Reporting Policies (Narrative) (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) plan $ / shares shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) 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