Stock-Based Compensation (Summary Of Activity Of Options Outstanding Not Yet Vested) (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-Based Compensation [Abstract]
Number of Shares, Unvested as of December 31, 2016	2,814
Number of Shares, Granted	1,171	1,357	1,076
Number of Shares, Vesting during period	(1,058)
Number of Shares, Forfeited	(67)
Number of Shares, Unvested as of December 31, 2017	2,860	2,814
Weighted-Average Fair Value Per Share, Unvested as of December 31, 2016	$ 20.62
Weighted-Average Fair Value Per Share, Granted	23.88	$ 19.19	$ 24.75
Weighted-Average Fair Value Per Share, Vesting during period	20.25
Weighted-Average Fair Value Per Share, Forfeited	21.23
Weighted-Average Fair Value Per Share, Unvested as of December 31, 2017	$ 22.08	$ 20.62