Investment and Disposition Activities - Additional Information (Detail)												1 Months Ended	6 Months Ended	7 Months Ended	12 Months Ended
	Feb. 18, 2016 USD ($)	Jan. 20, 2016 USD ($)	Jan. 08, 2016 USD ($)	Sep. 16, 2015 USD ($)	Jun. 26, 2015 USD ($)	Jun. 25, 2015 USD ($) Assets SecurityLoan	Jun. 01, 2015 USD ($)	Apr. 14, 2015 USD ($)	Feb. 05, 2015 USD ($)	Jan. 02, 2015 USD ($)	Dec. 09, 2014 USD ($)	May. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	Jul. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) Property	Dec. 31, 2013 USD ($)	Jan. 21, 2016 USD ($)	Jan. 15, 2016 USD ($)	Nov. 30, 2015 USD ($)	Oct. 09, 2015 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2012 USD ($)
Investment And Disposition Activities [Line Items]
Proceeds from sale of equity investments							$ 82,471,000							$ 200,000		$ 26,000
Distributions received													$ 4,959,000	705,000		14,618,000
Principal payment of loans											$ 27,394,000
Outstanding principal balance on loan receivable															$ 5,280,000	101,100,000						$ 24,005,000	$ 211,250,000
Investment in equity investments														$ 48,154,000		$ 30,341,000
Subsequent Event [Member] | First Purchase Agreement [Member]
Investment And Disposition Activities [Line Items]
Deposits money refundable	$ 1,500,000
Subsequent Event [Member] | Second Purchase Agreement [Member]
Investment And Disposition Activities [Line Items]
Buyer's deposit under the purchase contract	10,000,000
Gross proceeds from sale of real estate inclusive of forfeited deposits	90,000,000
Edens Center and Norridge Commons [Member]
Investment And Disposition Activities [Line Items]
Principal payment of loans									$ 15,275,000
Outstanding principal balance on loan receivable																					$ 97,000
Loan participation interest percentage																					30.00%
Minimum value of properties for entitlement to loan participation interest																					$ 115,000,000
Description of Trust's participation interest in loan															Upon satisfaction of the loan, the Trust was entitled to a participation interest equal to 30% of the value of both of the properties which collateralized the loan in excess of $115,000,000.
Loan receivable																				$ 3,100,000
Aggregate price in sale of general partnership interest															$ 493,000
Number of properties sold | Property															2
Vintage Housing Holdings [Member]
Investment And Disposition Activities [Line Items]
Additional contribution in equity investments										$ 5,645,000
Liquidation value of investment																						82,928,000
44 Monroe [Member] | Phoenix AZ [Member]
Investment And Disposition Activities [Line Items]
Ownership percentage in real estate investment								83.70%
Proceeds from sale of real estate, gross								$ 50,650,000
Proceeds from sale of real estate, net								$ 49,143,000
Liquidation value of property																						50,650,000
Concord Debt Holdings LLC [Member]
Investment And Disposition Activities [Line Items]
Distributions received												$ 20,173,000
CDH CDO LLC [Member]
Investment And Disposition Activities [Line Items]
Proceeds from sale of equity investments						$ 54,122,000
Number of bond assets sold | Assets						4
Number of loan asset sold | SecurityLoan						1
Amount received from the venture							$ 6,200,000
Cerritos [Member] | California [Member]
Investment And Disposition Activities [Line Items]
Proceeds from sale of real estate, gross				$ 30,500,000
Proceeds from sale of real estate, net				$ 6,174,000
Liquidation value of property																						29,916,000
Highgrove [Member] | Stamford, CT [Member] | First Purchase Agreement [Member]
Investment And Disposition Activities [Line Items]
Ownership percentage in real estate investment					83.70%
Proceeds from sale of real estate, gross					$ 90,000,000
Buyer's deposit under the purchase contract																			$ 1,000,000
Highgrove [Member] | Stamford, CT [Member] | Subsequent Event [Member] | First Purchase Agreement [Member]
Investment And Disposition Activities [Line Items]
Interest retained deposits																	$ 5,000,000
Buyer's deposit under the purchase contract																	$ 5,000,000
Deposit money returned	1,000,000
Highgrove [Member] | Stamford, CT [Member] | Subsequent Event [Member] | Second Purchase Agreement [Member]
Investment And Disposition Activities [Line Items]
Proceeds from sale of real estate, gross	$ 87,500,000
701 Seventh WRT Investor LLC [Member]
Investment And Disposition Activities [Line Items]
Additional capital contributions															$ 8,865,000
Capital contributions															$ 115,489,000
Sullivan Center, Chicago [Member] | Subsequent Event [Member]
Investment And Disposition Activities [Line Items]
Buyer's deposit under the purchase contract			$ 3,000,000
Investment in equity investments			$ 91,576,000
Sullivan Center, Chicago [Member] | Chicago, IL [Member]
Investment And Disposition Activities [Line Items]
Percentage of funded loan for retail tenant improvements and capital expenditure															100.00%
percentage of funded loan needed for office tenant improvements and capital expenditure															80.00%
Fund received for tenant improvements															$ 3,998,000
Accrued interest rate on loan funded															15.00%
Sullivan Center, Chicago [Member] | Chicago, IL [Member] | Subsequent Event [Member]
Investment And Disposition Activities [Line Items]
Fund received for tenant improvements																		$ 2,794,000
Lake Brandt, Greensboro, North Carolina [Member]
Investment And Disposition Activities [Line Items]
Liquidation value of investment															$ 20,000,000							$ 18,610,000
Lake Brandt, Greensboro, North Carolina [Member] | Subsequent Event [Member]
Investment And Disposition Activities [Line Items]
Proceeds from sale of real estate, gross		$ 20,000,000
Buyer's deposit under the purchase contract		$ 500,000