Stock-Based Compensation and Directors Stock Purchase Plan (Summary Of The Status Of Nonvested Share Awards) (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Nonvested Share Awards [Roll Forward]
Nonvested, share awards, beginning balance | shares	1,461,713
Granted, Shares | shares	263,123
Vested, Shares | shares	(442,435)
Forfeited, Shares | shares	(27,883)
Canceled, Shares | shares	0
Nonvested, share awards, ending balance | shares	1,254,518
Nonvested Weighted Average Grant Date Fair Value [Roll Forward]
Nonvested, Weighted Average Grant Date Fair Value, Beginning Balance | $ / shares	$ 33.02
Granted, Weighted Average Grant Date Fair Value | $ / shares	54.56
Vested, Weighted Average Grant Date Fair Value | $ / shares	29.41
Forfeited, Weighted Average Grant Date Fair Value | $ / shares	39.12
Canceled, Weighted Average Grant Date Fair Value | $ / shares	0.00
Nonvested , Weighted Average Grant Date Fair Value, Ending Balance | $ / shares	$ 38.67