Supplemental Detail for Certain Components of Consolidated Balance Sheets (Details 3) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Accounts payable and accrued expenses
Accrued costs on properties under development	$ 6,067	$ 8,595
Other items	19,771	21,122
Total accounts payable and accrued expenses	51,724	70,426
Other liabilities
Rent received in advance	15,092	20,929
Preferred units issued upon acquisition of ARCT	6,750
Security deposits	5,654	5,130
Total other liabilities	27,496	26,059
Note
Accounts payable and accrued expenses
Interest payable	22,973	40,061
Mortgages
Accounts payable and accrued expenses
Interest payable	$ 2,913	$ 648