Acquisitions, Dispositions, Leasing and Financing Activities (Details) (USD $)	0 Months Ended	3 Months Ended		9 Months Ended						9 Months Ended			9 Months Ended										9 Months Ended		9 Months Ended		9 Months Ended			9 Months Ended		9 Months Ended								9 Months Ended		9 Months Ended				9 Months Ended				9 Months Ended		0 Months Ended		9 Months Ended
	Aug. 06, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Aug. 23, 2012	Aug. 15, 2012	May 02, 2012	Dec. 31, 2011	Sep. 30, 2012 7.75% Senior Notes [Member]	Aug. 15, 2012 7.75% Senior Notes [Member]	Sep. 27, 2012 Office Space [Member] sqft	Sep. 30, 2012 10 Metrotech Loan LLC [Member]	Dec. 31, 2011 10 Metrotech Loan LLC [Member]	Sep. 30, 2012 River Road LLC [Member] Marc Realty [Member]	Dec. 31, 2011 River Road LLC [Member] Marc Realty [Member]	Sep. 30, 2012 Salt Creek LLC [Member] Marc Realty [Member]	Dec. 31, 2011 Salt Creek LLC [Member] Marc Realty [Member]	Sep. 30, 2012 900 Ridgebrook L L C [Member] Marc Realty [Member]	Dec. 31, 2011 900 Ridgebrook L L C [Member] Marc Realty [Member]	Mar. 23, 2012 Beneficial Interest Of Series D Cumulative Redeemable Preferred Shares [Member]	Sep. 27, 2012 B Note Portfolio Acquisition [Member] Unit Asset	Sep. 30, 2012 Burbank Centre B Note Portfolio Acquisition [Member]	Sep. 27, 2012 Burbank Centre B Note Portfolio Acquisition [Member]	Sep. 30, 2012 Pinnacle II B Note Portfolio Acquisition [Member]	Sep. 27, 2012 Pinnacle II B Note Portfolio Acquisition [Member] sqft	Sep. 30, 2012 Shops At Wailea B Note Portfolio Acquisition [Member]	Sep. 27, 2012 Shops At Wailea B Note Portfolio Acquisition [Member] sqft	Sep. 27, 2012 Shops At Wailea B Note Portfolio Acquisition [Member] Minimum [Member] Store	Sep. 30, 2012 Poipu Shopping Village B Note Portfolio Acquisition [Member]	Sep. 27, 2012 Poipu Shopping Village B Note Portfolio Acquisition [Member] sqft	Sep. 30, 2012 Riverside Equity Investment Loan Asset [Member]	Sep. 18, 2012 Riverside Equity Investment Loan Asset [Member]	Sep. 28, 2012 SoCal Lender - Equity Investment Loan Asset [Member]	Apr. 06, 2012 SoCal Lender - Equity Investment Loan Asset [Member]	Jan. 06, 2012 SoCal Lender - Equity Investment Loan Asset [Member] Unit	Jan. 06, 2012 SoCal Lender - Equity Investment Loan Asset [Member] Maximum [Member]	Jan. 06, 2012 SoCal Lender - Equity Investment Loan Asset [Member] Minimum [Member]	Jan. 06, 2012 SoCal Lender - Equity Investment Loan Asset [Member] Office Space [Member] sqft	Sep. 30, 2012 Westheimer [Member]	Sep. 17, 2012 Westheimer [Member] sqft	Sep. 30, 2012 Westheimer [Member] Maximum [Member]	Sep. 30, 2012 Westheimer [Member] Minimum [Member]	Sep. 30, 2012 Crossroads [Member]	Oct. 06, 2012 Crossroads [Member] sqft	Sep. 30, 2012 Waterford Place - Operating Property [Member]	Sep. 30, 2012 Waterford Place - Operating Property [Member] 320 Unit Class A multi-family Memphis, Tennessee [Member]	Jul. 19, 2012 Waterford Place - Operating Property [Member] 320 Unit Class A multi-family Memphis, Tennessee [Member]	Apr. 17, 2012 Waterford Place - Operating Property [Member] 320 Unit Class A multi-family Memphis, Tennessee [Member]	Sep. 30, 2012 223 West Jackson - Equity Investment [Member]	Jul. 02, 2012 223 West Jackson - Equity Investment [Member]	Feb. 03, 2012 Sullivan Center - Equity Investment Operating Property [Member] Venture sqft	Feb. 03, 2012 Sullivan Center - Equity Investment Operating Property [Member] First mortgage loan [Member]	Sep. 30, 2012 Memphis (Kroger) - Operating Property [Member]	Sep. 30, 2012 Indianapolis (Circle Tower) - Operating Property [Member]
Business Acquisition [Line Items]
Joint venture agreement date				Feb. 03, 2012
Number of joint venture entities																																																				2
Business acquisition cost of acquired entity face value																						$ 25,725,000		$ 10,000,000		$ 5,145,000		$ 7,719,000			$ 2,861,000					$ 798,000,000																$ 128,000,000
Mortgage loan outstanding principal amount																																																					140,300,000
Loans receivable accrued interest		793,000		793,000					500,000																																											6,886,000
Area of office and retail property																																																				942,000
Non-recourse mortgage loan																																																				100,000,000
Mezzanine loan face value																																																				47,458,000
Interest Holding Percentage																					0.0925																															0.50
Percentage of interest acquired								33.33%					33.33%
Outstanding loan amount		40,000,000		40,000,000									39,300,000																																		12,928,000
Negotiated lease term				10 years
Mortgage Loan Acquired Value													32,500,000
Mortgage loan		21,000,000		21,000,000																																												13,500,000
Mortgage loan extension right	2 years
Interest rate on mortgage loans	9.00%																						5.897%		6.313%		6.15%			6.618%
Leases expiring terms																							2014 and 2017		2021															April 30, 2018
New lease extensions date																																								Apr. 30, 2026
Negotiated lease term commencing date																																												Mar. 01, 2013
Purchase price of acquired entity																						20,696,000		9,000,000		4,631,000		5,154,000			1,911,000
Underwritten public offering				75,000,000
Due date of the notes										2022
Issue price, percentage of par value							100.00%
Net proceeds after deducting the underwriting discounts and commissions and estimated offering expenses										72,250,000
Redemption price policy										Redeem the Notes, in whole or in part, at any time or from time to time on or after August 15, 2015 at a redemption price in cash equal to 100% of the principal amount redeemed plus accrued and unpaid interest to, but not including, the redemption date.
Closing date of issuance of additional notes										Aug. 24, 2012
Net proceeds received										10,913,000
Gain on sale of equity investment		165,000	207,000	397,000	207,000
Acquisition price of the property																																																	21,473,000
Mortgage of the property																																																		9,500,000
Return of capital cash distribution																																																		3,524,000
Loan bears interest, description of variable rate basis				LIBOR plus 3%																																										LIBOR+2.5%
Maturity date of loan																							April 2017		September 2016		April 2017			January 2017										April 2016
Decreases annually subject to annual increases thereafter																																										5,478,000	4,260,000
Negotiated annual lease payments																																										8,255,000	7,974,000
Interest rate											7.75%
Equity investments		115,299,000		115,299,000					162,142,000				10,845,000			1,000,000				1,000,000
Area of collateralized building												421,990														230,000		166,000			40,800								4,500,000
Number of separate office																						4														31
Notes payment commencement date				Nov. 15, 2012
Loan bearing interest, terms				The loan bears interest at LIBOR +2.5% annually with a LIBOR floor of 0.5%, and requires monthly payments of principal and interest and matures on August 1, 2014, subject to two, one-year extensions. On the same date the Trust purchased an Interest Rate Cap which caps LIBOR at 0.5%.
Percentage of property occupied at acquisition																								100.00%		100.00%		97.00%			97.00%
Contribution to Trusts unconsolidated joint venture investment property																																																			3,524,000
B Note subordinate, senior financing		135,000,000		135,000,000																						84,701,000		108,055,000			28,932,000
Number of boutiques, shops, restaurants and galleries																													70
Termination of lease				Jun. 01, 2053
Proceeds from repurchase agreement																																		38,407,000
Equity recognized on repurchase agreement																																7,800,000
Percentage of owned joint venture																																	50.00%		10.2178%
Area of premises																																									614,000				53,000
Debt instrument, interest rate		2.50%		2.50%
LIBOR floor		0.005		0.005
Gain (loss) recognized upon repayment of loan																																0
Percentage of non-controlling ownership interest																																					73.00%	56.00%
Equity method investment, ownership percentage
Investment in equity investments				47,925,000	67,901,000								10,915,000
Common equity		33,077,000		33,077,000					33,041,000
Proceeds from sale of equity investments				2,297,000	6,000,000
Secured promissory note		238,097,000		238,097,000					230,940,000
Proceeds from sale of property																																																						600,000	6,300,000
Percentage of space of retail property leased																																																						100.00%
Cancellation fee paid on termination of lease																																																						600,000
Loss from discontinued operations																																																						50,000
Gain on sale of property																																																							945,000
Defeasance costs paid on satisfaction of debt																																																							574,000
Number of retail assets																						4
Owned Joint Venture																																				117,900,000
Repurchase of common shares outstanding		33,077,047		33,077,047					33,041,034
Repurchase facility																																				40,000,000
Net Proceeds After Orgination Fees Interest Reserve And Closing Expense																					77,572,000															38,100,000
Starwood Contribution																																			3,500,000
Effective interest in SoCal Loan																																			0.502
Generated Loan pay off																																		20,927,000
Trust allocable share																																			10,505,000
Public Offering																					3,220,000
Price Of Preference Share																					25.0385
par value																					$ 1
Preferred Shares Issued and Outstanding																					4,820,000
Acquisition Disposition Leasing and Financing Activities (Textual) [Abstract]
Additional Investment with Mack Cali Realty Corporation Venture		115,299,000		115,299,000					162,142,000				10,845,000			1,000,000				1,000,000
Percentage of leased property		90.00%		90.00%
Underwriters exercise over allotment option for the Notes						$ 11,250,000