Incentive Plan (Long-Term Incentive Units) (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term incentive units granted			195,073
Long-Term Incentive Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			4 years
Share/unit compensation expense	$ 2.0	$ 2.8	$ 9.9	$ 5.1
Capitalized expense related to construction and leasing activities	0.4	0.4	0.9	0.9
Unearned compensation	$ 12.7		$ 12.7		$ 12.9
Unearned compensation, period of recognition			2 years 4 months 24 days
Service And Performance Condition [Member] | Long-Term Incentive Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term incentive units granted				95,316
Number of shares satisfying the performance conditions				75,105