Incentive Plan (Summary Of Stock Options Outstanding And Exercisable) (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number outstanding	129,009	129,259
Weighted average remaining contractual life (years), Outstanding	3 years 2 months 12 days
Weighted average exercise price, Outstanding	$ 30.60
Aggregate intrinsic value, Outstanding	$ 4,684,052
$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 6 months 29 days
Weighted average exercise price, Outstanding	$ 12.00
Aggregate intrinsic value, Outstanding	1,914,712
$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 7 months 21 days
Weighted average exercise price, Outstanding	$ 21.28
Aggregate intrinsic value, Outstanding	775,740
$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	77,139
Weighted average remaining contractual life (years), Outstanding	4 years 18 days
Weighted average exercise price, Outstanding	$ 41.07
Aggregate intrinsic value, Outstanding	$ 1,993,600