Repurchases Of Common Stock (Schedule Of Common Stock Repurchases) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Equity [Abstract]
Shares repurchased in the open market (in shares)	302	312	1,284	1,398
Shares acquired through employee surrender for statutory tax withholding (in shares)	1	2	50	55
Total shares repurchased (in shares)	303	314	1,334	1,453
Cost of shares repurchased in the open market	$ 73,247	$ 50,413	$ 265,209	$ 215,320
Cost of shares for employee surrenders	390	370	9,110	7,829
Total cost of shares	$ 73,637	$ 50,783	$ 274,319	$ 223,149
Average cost per share - open market repurchases (in dollars per share)	$ 242.78	$ 161.57	$ 206.59	$ 153.99
Average cost per share - employee surrenders (in dollars per share)	253.34	155.14	181.68	142.15
Average cost per share - total (in dollars per share)	$ 242.83	$ 161.52	$ 205.65	$ 153.54