Investments in Joint Ventures (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Assets:
Other assets (1)	$ 5,579		$ 6,395
Total assets	329,904		2,168,836
Liabilities and members' equity:
Other liabilities	1,032		665
Liabilities and members' equity	329,904		2,168,836
Corporate Joint Venture [Member]
Assets:
Real estate assets, net	383,685		452,692
Other assets (1)	38,599	[1]	219,760	[1]
Total assets	422,284		672,452
Liabilities and members' equity:
Mortgages payable (1)	241,000	[1]	553,140	[1]
Other liabilities	78,685		90,255
Members' equity	102,599		29,057
Liabilities and members' equity	$ 422,284		$ 672,452

[1] The Bank of America Portfolio acquired a pool of treasury securities that defeased the mortgage loan that had previously encumbered the Bank of America Portfolio’s properties. The pledged government securities are U.S. Treasury bonds designated as defeasance collateral for mortgage notes payable of $0 and $312,140 as of June 30, 2013 and December 31, 2012, respectively.