Incentive Plan (Summary Of Restricted Stock Activity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Weighted-Average Grant Date Fair Value
Award vesting period	4 years
Restricted Stock
Units
Unvested beginning of period (shares)	264,995
Granted (shares)	130,746
Vested (shares)	(96,417)
Cancelled or expired (shares)	(2,838)
Unvested end of period (shares)	296,486
Weighted-Average Grant Date Fair Value
Unvested beginning of period ($ per share)	$ 61.45
Granted ($ per share)	80.40
Vested ($ per share)	61.05
Cancelled or expired ($ per share)	65.15
Unvested end of period ($ per share)	$ 65.04
Restricted stock expense	$ 0.9	$ 0.5
Capitalized expense related to construction and leasing activities	0.8	$ 0.7
Unearned compensation	$ 19.2		$ 10.4
Unearned compensation, period of recognition (in years)	1163 days
Restricted Stock | Maximum
Weighted-Average Grant Date Fair Value
Award vesting period	4 years