Equity Incentive Plans (Summary Of Restricted Share Unit Activity) (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($) $ / shares shares
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 | shares	390,441
Number of Shares, Granted | shares	300,752
Number of Shares, Vested | shares	(156,767)
Number of Shares, Outstanding at March 31, 2013 | shares	534,426
Weighted Average Grant Date Fair Value, Outstanding at December 31, 2012 | $ / shares	$ 54.84
Weighted Average Grant Date Fair Value, Granted | $ / shares	61.53
Weighted Average Grant Date Fair Value, Vested | $ / shares	52.73
Weighted Average Grant Date Fair Value, Outstanding at March 31, 2013 | $ / shares	$ 59.22
Weighted Average Life Remaining, Outstanding at March 31, 2013 (in years)	1 year 9 months 9 days
Range of settlement date for shares for non-employee trustee from grant date, minimum (in years)	1 year
Unamortized share-based compensation expense | $	$ 23,200
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 | shares	18,036
Number of Shares, Granted | shares	0
Number of Shares, Vested | shares	0
Number of Shares, Outstanding at March 31, 2013 | shares	18,036
Weighted Average Grant Date Fair Value, Outstanding at December 31, 2012 | $ / shares	$ 57.57
Weighted Average Grant Date Fair Value, Granted | $ / shares	0.00
Weighted Average Grant Date Fair Value, Vested | $ / shares	0.00
Weighted Average Grant Date Fair Value, Outstanding at March 31, 2013 | $ / shares	$ 57.57
Weighted Average Life Remaining, Outstanding at March 31, 2013 (in years)	1 month 12 days
Range of settlement date for shares for non-employee trustee from grant date, minimum (in years)	1 year
Unamortized share-based compensation expense | $	$ 87