Real Estate Investments - Discontinued Operations and Assets Held for Sale - Balance Sheet (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Balance Sheet data (as of the period ended):
Land	$ 165,325	$ 161,875
Buildings, improvements and lease intangibles	2,765,055	2,625,538
Personal property	9,217	8,739
Real estate properties, Total	2,956,651	2,821,323
Less accumulated depreciation	(610,402)	(580,617)
Total real estate properties, net	2,346,249	2,240,706
Other assets, net (including receivables)	155,961	126,962
Assets held for sale and discontinued operations, net	9,084	3,337
Accounts payable and accrued liabilities	57,610	65,678
Other liabilities	59,706	60,175
Liabilities of discontinued operations	1,024	131
Discontinued Operations [Member]
Balance Sheet data (as of the period ended):
Land	1,579	3,835
Buildings, improvements and lease intangibles	20,744	5,566
Personal property	0	207
Real estate properties, Total	22,323	9,608
Less accumulated depreciation	(13,350)	(6,303)
Total real estate properties, net	8,973	3,305
Other assets, net (including receivables)	111	32
Assets of discontinued operations, net	111	32
Assets held for sale and discontinued operations, net	9,084	3,337
Accounts payable and accrued liabilities	1,001	99
Other liabilities	23	32
Liabilities of discontinued operations	$ 1,024	$ 131