Incentive Plan (Class C Profits Interest Units) (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	May 01, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, shares outstanding	128,455,350	125,140,783
Class C Profit Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards satisfying market conditions on measurement date				593,316
Vesting based on market conditions with respect to the first measurement date not achieved	Of the Class C Units that satisfied the market condition on May 1, 2010, 60% vested on May 1, 2010 and the remaining 40% vested ratably each month through April 30, 2012.
Award vesting percentage, vested				60.00%
Award vesting percentage, unvested				40.00%
Approximate number of times simulation was run	100,000
Expected term	36 months
Expected volatility rate	23.00%
Risk-free interest rate	4.60%
Expected dividend rate	5.00%
Award limit, first market condition	$ 17
Award limit, second market condition	40
Common Stock, shares outstanding	69,200,000
Grant date fair value of awards	11.8
Requisite service period of share-based award	5 years
Stock option expense	0.5	2.0
Capitalized expense related to construction and leasing activities	0.1	0.3
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards satisfying market conditions on measurement date				20,169
Vesting based on market conditions with respect to the first measurement date not achieved	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.
Capitalized expense related to construction and leasing activities	$ 2.5	$ 2.1	$ 1.5