SEGMENT REPORTING - Net Real Estate and Secured Note Payable Balances (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Segment Reporting Information [Line Items]
Net Real Estate	$ 1,806,879		$ 1,775,400
Secured Notes Payable	718,253	[1]	819,983	[1]
Total Retail
Segment Reporting Information [Line Items]
Net Real Estate	634,758		639,456
Secured Notes Payable	60,518	[1]	161,975	[1]
Total Office
Segment Reporting Information [Line Items]
Net Real Estate	767,271		757,854
Secured Notes Payable	425,981	[1]	426,254	[1]
Total Multifamily
Segment Reporting Information [Line Items]
Net Real Estate	210,569		182,468
Secured Notes Payable	101,444	[1]	101,444	[1]
Total Mixed-Use
Segment Reporting Information [Line Items]
Net Real Estate	194,281		195,622
Secured Notes Payable	$ 130,310	[1]	$ 130,310	[1]

[1] Excludes unamortized fair market value adjustments of $6.4 million and $7.2 million as of March 31, 2015 and December 31, 2014, respectively.