Real Estate Investments - Discontinued Operations and Assets Held for Sale - Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Balance Sheet data (as of the period ended):
Land	$ 186,108	$ 183,060
Buildings, improvements and lease intangibles	3,042,367	3,048,251
Personal property	9,833	9,914
Real estate properties, Total	3,271,238	3,258,279
Accumulated depreciation	(737,398)	(700,671)
Total real estate properties, net	2,533,840	2,557,608
Other assets, net (including receivables)	192,969	185,337
Assets held for sale and discontinued operations, net	6,380	9,146
Liabilities of discontinued operations	216	372
Discontinued Operations [Member]
Balance Sheet data (as of the period ended):
Land	2,524	422
Buildings, improvements and lease intangibles	10,728	12,822
Personal property	7	13
Real estate properties, Total	13,259	13,257
Accumulated depreciation	(6,928)	(4,464)
Total real estate properties, net	6,331	8,793
Other assets, net (including receivables)	49	353
Assets of discontinued operations, net	49	353
Assets held for sale and discontinued operations, net	6,380	9,146
Accounts payable and accrued liabilities	175	86
Other liabilities	41	286
Liabilities of discontinued operations	$ 216	$ 372