Related-Party Transactions - Fees and Reimbursements Paid by the Trust (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Related Party Transaction [Line Items]
Fees and reimbursements paid by the Trust	$ 2,773	$ 2,679
Base Asset Management Fee [Member]
Related Party Transaction [Line Items]
Fees and reimbursements paid by the Trust	2,375	2,266
Property Management Fee [Member]
Related Party Transaction [Line Items]
Fees and reimbursements paid by the Trust	319	282
Construction Management Fee [Member]
Related Party Transaction [Line Items]
Fees and reimbursements paid by the Trust	$ 79	$ 131