Equity Incentive Plans (Summary Of Restricted Share Unit Activity) (Details) - Jun. 30, 2015 - USD ($) $ / shares in Units, $ in Thousands	Total
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Number of Shares, Outstanding at December 31, 2012	468,451
Number of Shares, Granted	206,185
Number of Shares, Vested	(295,487)
Number of Shares, Outstanding at March 31, 2013	378,341
Weighted Average Grant Date Fair Value, Outstanding at December 31, 2012	$ 49.29
Weighted Average Grant Date Fair Value, Granted	61.33
Weighted Average Grant Date Fair Value, Vested	50.37
Weighted Average Grant Date Fair Value, Outstanding at March 31, 2013	$ 55.00
Weighted Average Life Remaining, Outstanding at March 31, 2013 (in years)	1 year 5 months 15 days
Range of settlement date for shares for non-employee trustee from grant date, minimum (in years)	1 year
Unamortized share-based compensation expense	$ 15,000
Restricted Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Number of Shares, Outstanding at December 31, 2012	19,685
Number of Shares, Granted	18,036
Number of Shares, Vested	(19,685)
Number of Shares, Outstanding at March 31, 2013	18,036
Weighted Average Grant Date Fair Value, Outstanding at December 31, 2012	$ 53.55
Weighted Average Grant Date Fair Value, Granted	57.57
Weighted Average Grant Date Fair Value, Vested	53.55
Weighted Average Grant Date Fair Value, Outstanding at March 31, 2013	$ 57.57
Weighted Average Life Remaining, Outstanding at March 31, 2013 (in years)	10 months 15 days
Range of settlement date for shares for non-employee trustee from grant date, minimum (in years)	1 year
Unamortized share-based compensation expense	$ 865