Related-Party Transactions - Fees and Reimbursements Paid by the Trust (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Related Party Transaction [Line Items]
Fees and reimbursements paid by the Trust	$ 1,999	$ 2,773
Base Asset Management Fee [Member]
Related Party Transaction [Line Items]
Fees and reimbursements paid by the Trust	1,684	2,375
Property Management Fee [Member]
Related Party Transaction [Line Items]
Fees and reimbursements paid by the Trust	284	319
Construction Management Fee [Member]
Related Party Transaction [Line Items]
Fees and reimbursements paid by the Trust	$ 31	$ 79