Acquisitions, Dispositions, and Mortgage Funding (Details 1) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Balance Sheet data (as of the period ended):
Land	$ 164,649	$ 161,875
Buildings, improvements and lease intangibles	2,613,069	2,625,538
Personal property	19,208	19,100
Real estate properties, Total	2,813,980	2,831,684
Less accumulated depreciation	(597,434)	(586,725)
Total real estate properties, net	2,216,546	2,244,959
Other assets, net (including receivables)	132,102	122,709
Assets held for sale and discontinued operations, net	22,297	3,337
Accounts payable and accrued liabilities	45,534	65,678
Other liabilities	57,895	60,175
Liabilities of discontinued operations	86	131
Discontinued Operations [Member]
Balance Sheet data (as of the period ended):
Land	4,310	3,835
Buildings, improvements and lease intangibles	35,342	5,566
Personal property	215	212
Real estate properties, Total	39,867	9,613
Less accumulated depreciation	(17,805)	(6,303)
Total real estate properties, net	22,062	3,310
Other assets, net (including receivables)	235	27
Assets of discontinued operations, net	235	27
Assets held for sale and discontinued operations, net	22,297	3,337
Accounts payable and accrued liabilities	71	99
Other liabilities	15	32
Liabilities of discontinued operations	$ 86	$ 131