Segment Reporting (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Jan. 19, 2011
Net Real Estate and Secured note payable balances by Segments
Net Real Estate	$ 1,698,495	$ 1,452,681
Secured Notes Payable	964,068	943,479	342,000
Retail [Member]
Net Real Estate and Secured note payable balances by Segments
Net Real Estate	652,766	655,450
Secured Notes Payable	398,404	400,320
Office [Member]
Net Real Estate and Secured note payable balances by Segments
Net Real Estate	804,811	551,955
Secured Notes Payable	347,635	327,331
Multifamily [Member]
Net Real Estate and Secured note payable balances by Segments
Net Real Estate	36,587	37,187
Secured Notes Payable	101,444	101,444
Mixed-Use [Member]
Net Real Estate and Secured note payable balances by Segments
Net Real Estate	204,331	208,089
Secured Notes Payable	$ 130,310	$ 130,310