Stock-Based Compensation and Directors Stock Purchase Plan (Summary Of SAR Activity) (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Stock Appreciation Rights, Shares [Roll Forward]
Outstanding, Shares, Beginning Balance | shares	1,390,782
Granted, Shares | shares	173,740
Forfeited, Shares | shares	(13,325)
Expired, Shares | shares	(878)
Exercised, Shares | shares	(371,033)
Outstanding, Shares, Ending Balance | shares	1,179,286
Exercisable, Shares, Ending Balance | shares	630,135
Stock Appreciation Rights, Weighted Average Exercise Price [Roll Forward]
Outstanding, Weighted Average Exercise Price, Beginning Balance | $ / shares	$ 32.89
Granted, Weighted Average Exercise Price | $ / shares	54.79
Forfeited, Weighted Average Exercise Price | $ / shares	42.19
Expired, Weighted Average Exercise Price | $ / shares	34.75
Exercised, Weighted Average Exercise Price | $ / shares	29.30
Outstanding, Weighted Average Exercise Price, Ending Balance | $ / shares	37.13
Exercisable, Weighted Average Exercise Price, Ending Balance | $ / shares	$ 32.60
Outstanding, Weighted Average Remaining Contractual Term (in years)	6 years 2 months
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding | $	$ 22,073
Exercisable, Weighted Average Remaining Contractual Term (in years)	4 years 7 months
Exercisable, Aggregate Intrinsic Value, Ending Balance | $	$ 14,645