Stockholders' Equity (Schedule Of Common Stock Activity) (Details)	12 Months Ended
	Dec. 31, 2017 shares
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock Issued, Beginning Balance (in shares)	206,182,213
Common Stock Outstanding, Beginning Balance (in shares)	202,087,672
Restricted stock issued (in shares)	1,391,588
Repurchase of common stock (in shares)	(71,598,013)
Shares held to cover taxes on vesting restricted shares and other (in shares)	(583,013)
Employee stock purchase plan participation (in shares)	54,690
Common Stock Issued, Ending Balance (in shares)	207,628,491
Common Stock Outstanding, Ending Balance (in shares)	131,352,924
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock Issued, Beginning Balance (in shares)	206,182,213
Restricted stock issued (in shares)	1,391,588
Employee stock purchase plan participation (in shares)	54,690
Common Stock Issued, Ending Balance (in shares)	207,628,491
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock Outstanding, Beginning Balance (in shares)	(4,094,541)
Repurchase of common stock (in shares)	(71,598,013)
Shares held to cover taxes on vesting restricted shares and other (in shares)	(583,013)
Common Stock Outstanding, Ending Balance (in shares)	(76,275,567)