Repurchases Of Common Stock (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares
Shares of common stock repurchases authorized	68,000
Remaining shares available for repurchase under authorization	5,000
Share repurchases during the period	1,749	3,071	5,659
Shares acquired through employee surrenders	57	60	69
Total shares repurchased	1,806	3,131	5,728
Cost of share repurchases during the period | $	$ 270,297	$ 313,072	$ 406,430
Cost of employee surrenders | $	8,074	4,372	5,457
Total cost of shares repurchased | $	$ 278,371	$ 317,444	$ 411,887
Treasury Stock Acquired Average Cost Per Share, Open Market Repurchase | $ / shares	$ 154.51	$ 101.96	$ 71.82
Average cost per share - employee surrenders | $ / shares	142.55	73.04	72.55
Average cost per share | $ / shares	$ 154.13	$ 101.40	$ 71.90
Stock split			2
Treasury Stock [Member]
Total shares repurchased			4,300