Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands, shares in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019
Summary Of Significant Accounting Policies [Line Items]
Cash equivalents	$ 265,400	$ 581,400
Provision for doubtful accounts	$ 1,712	$ 1,697	$ 0
Anti-dilutive securities to purchase common shares	0.0	0.6	0.4
Compensation cost recognized for stock-based awards	$ 10,100	$ 7,800	$ 5,300
Income tax benefit recognized in the income statement for stock-based awards	2,400	2,800	1,100
Total cash received as a result of stock option exercises	3,600	11,200	18,800
Tax benefit realized as a result of stock option exercises and the vesting of other share-based awards	2,500	5,000	3,700
Total intrinsic value of stock options exercised	2,300	7,700	5,100
Exchange losses related to foreign currency transactions	$ 1,000	$ 2,100	$ 500
Minimum [Member] | Buildings And Building Improvements [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful lives of the assets	5 years
Minimum [Member] | Machinery And Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful lives of the assets	2 years
Minimum [Member] | Furniture And Fixtures [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful lives of the assets	2 years
Minimum [Member] | Vehicles [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful lives of the assets	2 years
Maximum [Member] | Buildings And Building Improvements [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful lives of the assets	40 years
Maximum [Member] | Machinery And Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful lives of the assets	15 years
Maximum [Member] | Furniture And Fixtures [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful lives of the assets	12 years
Maximum [Member] | Vehicles [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful lives of the assets	8 years
Accounting Standards Update 2016-02 Member | Minimum [Member] | Scenario Forecast [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating Lease Right Of Use Asset				$ 85,000
Operating Lease Liability				85,000
Accounting Standards Update 2016-02 Member | Maximum [Member] | Scenario Forecast [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating Lease Right Of Use Asset				90,000
Operating Lease Liability				$ 90,000