Shareholders' Equity (Narrative) (Details) - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Dividends declared	$ (108,489,000)	$ (110,046,000)	$ (122,240,000)
Stock repurchases	$ 302,473,000	$ 916,323,000	$ 603,206,000
Share repurchase plan [Member]
Class of Stock [Line Items]
Shares repurchased under authorized repurchase programs	10.9	35.4	30.9
Stock repurchases	$ 294,559,000	$ 910,300,000	$ 600,000,000.0
Remaining value of stock repurchase programs authorization	299,900,000
Shares withheld to pay taxes [Member]
Class of Stock [Line Items]
Stock repurchases	$ 7,900,000	$ 6,000,000.0	$ 3,200,000