Repurchases Of Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Repurchases Of Common Stock [Abstract]
Shares repurchased in the open market	696	269	1,086	977
Shares acquired through employee surrender for statutory tax withholding	1	2	53	54
Total shares repurchased	697	271	1,139	1,031
Cost of shares repurchased in the open market	$ 114,163	$ 23,260	$ 164,907	$ 72,975
Cost of shares for employee surrenders	156	203	7,459	3,732
Total cost of shares	$ 114,319	$ 23,463	$ 172,366	$ 76,707
Average cost per share - open market repurchase	$ 163.96	$ 86.45	$ 151.81	$ 74.68
Average cost per share - employee surrenders	168.25	88.18	141.56	68.82
Average cost per share - total	$ 163.97	$ 86.46	$ 151.34	$ 74.38