Incentive Plan (Class C Profits Interest Units) (Narrative) (Details) (USD $)	0 Months Ended	3 Months Ended		9 Months Ended
	May 01, 2010	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, shares outstanding		123,261,390		123,261,390		106,039,279
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% will vest ratably each month thereafter for 24 months.
Award vesting percentage, vested	60.00%
Award vesting percentage, unvested	40.00%
Award vesting, expected term	24 months
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				$ 17,000,000
Award limit, second market condition				40,000,000
Common Stock, shares outstanding		69,200,000		69,200,000
Grant date fair value of awards				11,800,000
Requisite service period of share-based award				5 years
Unearned compensation		0		0		600,000
Stock option expense		0	700,000	500,000	1,600,000
Capitalized expense related to construction and leasing activities		0	100,000	100,000	200,000
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.
Unearned compensation		8,800,000		8,800,000		5,500,000
Capitalized expense related to construction and leasing activities		$ 600,000	$ 400,000	$ 1,500,000	$ 1,100,000