Shareholders' Equity (Narrative) (Details) - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 25, 2018
Class of Stock [Line Items]
Dividends declared	$ 110,046,000	$ 122,240,000	$ 117,873,000
Stock repurchases	$ 916,323,000	$ 603,206,000	$ 442,738,000
Share repurchase plan [Member]
Class of Stock [Line Items]
Shares repurchased under authorized repurchase programs	35.4	30.9	21.2
Stock repurchases	$ 910,300,000	$ 600,000,000	$ 433,690,000
Remaining value of stock repurchase programs authorization	94,400,000
Shares withheld to pay taxes [Member]
Class of Stock [Line Items]
Stock repurchases	$ 6,000,000	$ 3,200,000	$ 9,000,000
Subsequent Event [Member] | Share repurchase plan [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount				$ 500,000,000