Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2017
Summary Of Significant Accounting Policies [Line Items]
Cash equivalents	$ 581,400	$ 531,800
Provision to accounts receivable	$ 1,700
Anti-dilutive options to purchase common shares	0.6	0.4	1.3
Compensation cost recognized for stock-based awards	$ 7,800	$ 5,300	$ 7,700
Income tax benefit recognized in the income statement for stock-based awards	2,800	1,100	$ 3,100
Weighted-average fair value per option granted			$ 8.76
Total cash received as a result of stock option exercises	11,200	18,800	$ 2,000
Tax benefit realized as a result of stock option exercises and the vesting of other share-based awards	5,000	3,700	2,100
Total intrinsic value of stock options exercised	7,700	5,100	700
Exchange losses related to foreign currency transactions	2,100	500	2,300
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reclassification from cash flows from financing activities	(31,352)	(35,310)	159,066
Reclassification to cash flows from operating activities	$ 145,842	273,088	147,375
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 2016-09 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reclassification from cash flows from financing activities		600	600
Reclassification to cash flows from operating activities		$ 600	$ 600
Accounting Standards Update 2016-09 [Member] | Retained Earnings [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net cumulative effect adjustment				$ (200)
Accounting Standards Update 2016-09 [Member] | Additional Paid In Capital [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net cumulative effect adjustment				$ 200
Accounting Standards Update 201409 [Member] | Preliminary assessment [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Effect of Change on Diluted Earnings Per Share	$ 0.02	$ (0.02)