Repurchases Of Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Repurchases Of Common Stock [Abstract]
Shares repurchased in the open market	312	142	1,398	1,119
Shares acquired through employee surrender for statutory tax withholding	2	2	55	56
Total shares repurchased	314	144	1,453	1,175
Cost of shares repurchased in the open market	$ 50,413	$ 15,260	$ 215,320	$ 88,235
Cost of shares for employee surrenders	370	218	7,829	3,950
Total cost of shares	$ 50,783	$ 15,478	$ 223,149	$ 92,185
Average cost per share - open market repurchase	$ 161.57	$ 107.38	$ 153.99	$ 78.84
Average cost per share - employee surrenders	155.14	112.91	142.15	70.33
Average cost per share - total	$ 161.52	$ 107.46	$ 153.54	$ 78.43