Incentive Plan (Long-Term Incentive Units) (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term incentive units granted	192,242	166,080	184,542
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	85,910
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%
Award vesting period	4 years
Share/unit compensation expense	$ 8.9	$ 9.0	$ 8.7
Capitalized expense related to construction and leasing activities	1.6	1.1	0.8
Unearned compensation	$ 12.9	$ 13.3
Unearned compensation, period of recognition	2 years 6 months
Service And Performance Condition [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term incentive units granted	95,316
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	86,843	98,632
Number of shares satisfying the performance conditions	75,105	78,118