Incentive Plan (Restricted Stock) (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Service conditions of the awards			The service conditions of the awards provide for 20% vesting on each of the first and second anniversaries of the grant date and 30% vesting on each of the third and fourth anniversaries of the grant date
Service and Performance Condition [Member] | Restricted Stock [Member]
Restricted shares granted			50,999	37,914
Restricted Stock [Member]
Restricted shares granted			40,807	31,164
Restricted stock, vesting period (years)			four
Restricted Stock Expense	$ 0.5	$ 0.4	$ 1.0	$ 0.7
Capitalized expense related to construction and leasing activities	0.4	0.3	0.7	0.4
Unearned compensation due to the unvested portion of restricted stock			$ 7.1		$ 4.2
Period of recognition of unearned compensation (years)			3.2