Incentive Plan (Long-Term Incentive Units) (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term incentive units granted			192,242
Long-Term Incentive Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term incentive units granted			89,769	79,237
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, provided the grantee continues employment on each anniversary date.
Vesting percentage, first and second anniversaries			20.00%
Vesting percentage, third and fourth anniversaries			30.00%
Share/unit compensation expense			$ 2.1	$ 7.2
Capitalized expense related to construction and leasing activities	0.4	0.4	1.3	0.8
Unearned compensation	$ 16.3		$ 16.3		$ 13.3
Unearned compensation, period of recognition			2 years 8 months 12 days
Service And Performance Condition [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term incentive units granted			95,316	86,843
Service And Performance Condition [Member] | Long-Term Incentive Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares satisfying the performance conditions			78,118
Minimum [Member] | Long-Term Incentive Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			3 years
Maximum [Member] | Long-Term Incentive Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			5 years