Acquisition and Disposition Activities - Loan Asset Activity - Additional Information (Detail) (USD $)	0 Months Ended		7 Months Ended	12 Months Ended		0 Months Ended		12 Months Ended	0 Months Ended		3 Months Ended	0 Months Ended
	Dec. 09, 2014	Feb. 07, 2014	Jul. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 22, 2014	Mar. 05, 2014	Dec. 31, 2014	Jul. 07, 2014	Jan. 10, 2014	Mar. 31, 2014	Aug. 07, 2014	Aug. 06, 2014	Aug. 01, 2014	Jun. 01, 2012
Business Acquisition [Line Items]
Outstanding loans acquired for aggregate price			$ 31,492,000	$ 21,437,000	$ 163,800,000
Ownership percentage															20.00%
Payment of interest accrued			15,280,000	23,735,000	16,467,000
Principal payments received on loan receivable	27,394,000
Distributions received from equity investments	6,565,000
Net proceeds	33,959,000
Liquidation value of investment														29,369,000
Sales of interest		42,900,000
Sale price net amount		29,150,000
Gain (loss) on sale of loan		0
Pinnacle II [Member]
Business Acquisition [Line Items]
Liquidation value of investment														4,989,000
Proceeds from sale of real estate, gross						5,017,000
Proceeds from sale of real estate, net						4,967,000
Edens Center and Norridge Commons [Member]
Business Acquisition [Line Items]
Loan secured by limited partnership interests, face amount							15,500,000
Loan secured by limited partnership interests, basis spread on variable rate							12.00%
Loan secured by limited partnership interests, increase in basis spread on variable rate in each extended term							1.00%
Loan secured by limited partnership interests, stated current interest rate							10.00%
Loan secured by limited partnership interests, annual increase in stated current interest rate							0.50%
Loan secured by limited partnership interests, term								3 years
Description of Trust's participation interest in loan								Upon satisfaction of the loan, the Trust will be entitled to a participation interest equal to the greater of (i) a 14.5% internal rate of return ("IRR") (increasing to 15.5% IRR after the initial term) and (ii) 30% (increasing to 40% after the initial term and 50% after the first extended term) of the value of the properties in excess of $115,000,000.
Loan participation interest IRR percentage							14.50%
Loan participation interest IRR percentage after initial term							15.50%
Loan participation interest percentage							30.00%
Loan participation interest percentage after initial term							40.00%
Loan participation interest percentage after extended term							50.00%
Minimum value of properties for entitlement to loan participation interest							115,000,000
Playa Vista Mezzanine Loan [Member]
Business Acquisition [Line Items]
Mortgage loan on real estate, increase in principal balance										4,000,000
Mortgage loan on real estate, increase in interest rate										1.50%
Mortgage loan on real estate, revised interest rate										16.25%
Mortgage loan on real estate, share in increased loan amount										2,000,000
Share funded amount										1,992,000
Outstanding loans acquired for aggregate price									14,000,000
Ownership percentage									50.00%
Payment of interest accrued									108,000
Premium amount included in purchase price									762,000
Legacy Orchard Loan [Member]
Business Acquisition [Line Items]
Retained interest		2.50%
Hotel Wales Loan [Member]
Business Acquisition [Line Items]
Retained interest		0.50%
Queensridge [Member]
Business Acquisition [Line Items]
Aggregate principal payments											2,908,000
Trust received, exit fee											1,787,000
The Shops at Wailea [Member]
Business Acquisition [Line Items]
Net proceeds from loan repayment												7,556,000
Liquidation value of investment												7,516,000
Office [Member] | Stamford [Member]
Business Acquisition [Line Items]
Net proceeds from distributions of venture													$ 9,450,000
Number of office properties													7