Loans Receivable - Summary of Trust's Loans Receivable (Parenthetical) (Detail) (USD $)	0 Months Ended	12 Months Ended
	Dec. 09, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount at par value of loan receivable		$ 22,607,000
Principal payment of loans	27,394,000
Outstanding principal balance of loans		24,005,000	101,100,000	211,250,000	114,333,000
Mezzanine [Member] | Edens Center and Norridge Commons [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount at par value of loan receivable		15,500,000
Amount to be collected on participating interest of loans		3,000,000
Principal payment of loans		15,275,000
Outstanding principal balance of loans		$ 225,000
LIBOR floor, percentage		0.50%