Summary Of Significant Accounting Policies (Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Net income	$ 259,251	$ 265,636	$ 252,521
Weighted average shares outstanding - basic	84,988	87,227	89,561
Dilutive effect of stock plans	1,866	1,742	1,941
Weighted average shares outstanding - diluted	86,854	88,969	91,502
Basic earnings per share	$ 3.05	$ 3.05	$ 2.82
Diluted earnings per share	$ 2.98	$ 2.99	$ 2.76
Anti-dilutive shares	84	260	206