Related-Party Transactions (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Fees and reimbursements paid by the Trust
Fees and reimbursements paid by the Trust	$ 2,679	$ 2,143
Base Asset Management [Member]
Fees and reimbursements paid by the Trust
Fees and reimbursements paid by the Trust	2,266	2,027
Property Management [Member]
Fees and reimbursements paid by the Trust
Fees and reimbursements paid by the Trust	282	116
Construction Management [Member]
Fees and reimbursements paid by the Trust
Fees and reimbursements paid by the Trust	$ 131