Related-Party Transactions - Fees and Reimbursements Paid by the Trust (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Related Party Transaction [Line Items]
Fees and reimbursements paid by the Trust	$ 2,847	$ 2,738	$ 5,620	$ 5,417
Base Asset Management Fee [Member]
Related Party Transaction [Line Items]
Fees and reimbursements paid by the Trust	2,399	2,291	4,774	4,557
Property Management Fee [Member]
Related Party Transaction [Line Items]
Fees and reimbursements paid by the Trust	338	309	657	591
Construction Management Fee [Member]
Related Party Transaction [Line Items]
Fees and reimbursements paid by the Trust	$ 110	$ 138	$ 189	$ 269