SEGMENT REPORTING - Net Real Estate and Secured Note Payable Balances (Details) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net Real Estate		$ 1,837,096	$ 1,775,400
Secured Notes Payable	[1]	584,437	819,983
Total Retail
Segment Reporting Information [Line Items]
Net Real Estate		625,138	639,456
Secured Notes Payable	[1]	60,222	161,975
Total Office
Segment Reporting Information [Line Items]
Net Real Estate		771,370	757,854
Secured Notes Payable	[1]	292,461	426,254
Total Multifamily
Segment Reporting Information [Line Items]
Net Real Estate		248,804	182,468
Secured Notes Payable	[1]	101,444	101,444
Total Mixed-Use
Segment Reporting Information [Line Items]
Net Real Estate		191,784	195,622
Secured Notes Payable	[1]	$ 130,310	$ 130,310

[1] Excludes unamortized fair market value adjustments of $5.0 million and $7.2 million as of September 30, 2015 and December 31, 2014, respectively.