Stock-Based Compensation (Summary Of The Status Of Nonvested Share Awards) (Details)	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Nonvested Share Awards [Roll Forward]
Nonvested, Shares, Beginning Balance | shares	1,254,518
Granted, Shares | shares	197,883
Vested, Shares | shares	(266,058)
Forfeited, Shares | shares	(2,604)
Nonvested, Shares, Ending Balance | shares	1,183,739
Nonvested, Weighted Average Grant Date Fair Value, Beginning Balance | $ / shares	$ 38.67
Granted , Weighted Average Grant Date Fair Value | $ / shares	58.45
Vested , Weighted Average Grant Date Fair Value | $ / shares	32.56
Forfeited , Weighted Average Grant Date Fair Value | $ / shares	49.62
Nonvested , Weighted Average Grant Date Fair Value, Ending Balance | $ / shares	$ 43.33