Stock-Based Compensation (Summary Of SAR Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Stock Appreciation Rights [Roll Forward]
Outstanding, Shares	1,151,699	1,179,286
Granted, Shares	168,716
Forfeited, Shares	(323)
Expired, Shares	0
Exercised, Shares	(195,980)
Outstanding, Weighted Average Exercise Price, Beginning Balance	$ 37.13
Granted, Weighted Average Exercise Price	58.42
Forfeited, Weighted Average Exercise Price	37.52
Expired, Weighted Average Exercise Price	0.00
Exercised, Weighted Average Exercise Price	28.93
Outstanding, Weighted Average Exercise Price, Ending Balance	$ 41.65
Outstanding, Weighted Average Remaining Contractual Term (in years)	7 years 5 months
Outstanding, Aggregate Intrinsic Value, Ending Balance	$ 21,035