Loans Receivable - Summary of Trust's Loans Receivable (Parenthetical) (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, accrued interest	$ 27,000	$ 218,000
Edens Center and Norridge Commons [Member] | Mezzanine [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount to be collected on participating interest of loans	3,000,000	3,000,000
Loans receivable, accrued interest	$ 1,000	$ 1,000
LIBOR floor, percentage	0.50%