Related-Party Transactions (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fees and reimbursements paid by the Trust
Fees and reimbursements paid by the Trust	$ 9,805	$ 8,228	$ 5,368
Base Asset Management Fee [Member]
Fees and reimbursements paid by the Trust
Fees and reimbursements paid by the Trust	8,953	7,690	5,225
WRP Sub-Management LLC Credit [Member]
Fees and reimbursements paid by the Trust
Fees and reimbursements paid by the Trust			(129)
Property Management Fee [Member]
Fees and reimbursements paid by the Trust
Fees and reimbursements paid by the Trust	724	537	248
Construction Management Fee [Member]
Fees and reimbursements paid by the Trust
Fees and reimbursements paid by the Trust	$ 128	$ 1	$ 24