Incentive Plan (Summary Of Stock Options Outstanding And Exercisable) (Details) (USD $)	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number outstanding	128,007	129,259
Weighted average remaining contractual life (years), Outstanding	2 years 11 months 9 days
Weighted average exercise price, Outstanding	$ 30.51
Aggregate intrinsic value, Outstanding	$ 3,902,300
$12.00-13.02 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price, lower limit	$ 12.00
Exercise price, upper limit	$ 13.02
Number outstanding	34,870
Weighted average remaining contractual life (years), Outstanding	1 year 3 months 29 days
Weighted average exercise price, Outstanding	$ 12.00
Aggregate intrinsic value, Outstanding	1,708,630
$20.37-28.09 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price, lower limit	$ 20.37
Exercise price, upper limit	$ 28.09
Number outstanding	17,000
Weighted average remaining contractual life (years), Outstanding	2 years 4 months 21 days
Weighted average exercise price, Outstanding	$ 21.28
Aggregate intrinsic value, Outstanding	675,270
$33.18-41.73 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price, lower limit	$ 33.18
Exercise price, upper limit	$ 41.73
Number outstanding	76,137
Weighted average remaining contractual life (years), Outstanding	3 years 9 months 18 days
Weighted average exercise price, Outstanding	$ 41.06
Aggregate intrinsic value, Outstanding	$ 1,518,400