Incentive Plan (Long Term Incentive Units) (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
Long-term incentive units granted			183,505
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
Minimum [Member] | Long Term Incentive Units [Member]
Long-term incentive units vesting period (years)			4
Service and Performance Condition [Member] | Long Term Incentive Units [Member]
Long-term incentive units granted			98,632	107,993
Long Term Incentive Units [Member]
Long-term incentive units granted			84,873	92,368
Long-term incentive units vesting period			four
Long-term incentive units expense	$ 2.5	$ 2.2	$ 4.4	$ 3.4
Capitalized expense related to construction and leasing activities	0.2	0.2	0.4	0.5
Unearned compensation due to the unvested portion of restricted stock			$ 18.2		$ 12.9
Period of recognition of unearned compensation (years)			2.8