Noncontrolling Interests - Outstanding Cumulative Redeemable Preferred Units (Details) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013
Preferred Units [Line Items]
Preferred stock redemption premium	$ (1,236,000)	$ (1,236,000)
Series E Preferred Stock [Member]
Preferred Units [Line Items]
Stock Redeemed or Called During Period, Value	20,000,000
Preferred Stock, Dividend Rate, Percentage	7.00%
Series F Preferred Stock [Member]
Preferred Units [Line Items]
Stock Redeemed or Called During Period, Value	17,500,000
Preferred Stock, Dividend Rate, Percentage	6.65%
Series G Preferred Stock [Member]
Preferred Units [Line Items]
Stock Redeemed or Called During Period, Value	$ 27,000,000
Preferred Stock, Dividend Rate, Percentage	6.70%