Commitments and Contingencies - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Lease	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Land Lease Communities [Member] Community	Dec. 31, 2012 Ground Lease One [Member]	Dec. 31, 2012 Ground Lease Two [Member]	Dec. 31, 2012 Operating Leases [Member]	Dec. 31, 2010 Post Pentagon Row [Member]	Jun. 30, 2011 Post Renaissance [Member]
Commitments And Contingencies [Line Items]
Number of ground leases	2
Number of operating communities				2
Lease expiration term					2038	2074	2057
Rent expense	$ 3,738	$ 3,691	$ 5,202
Purchase price to acquire ownership property								8,800	6,670
Reimbursement of ground lease payments			$ 723