Real Estate Investments - Discontinued Operations and Assets Held for Sale - Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Balance Sheet data (as of the period ended):
Land	$ 201,090	$ 201,283
Buildings, improvements and lease intangibles	3,600,826	3,601,460
Personal property	10,205	10,314
Real estate properties, Total	3,847,234	3,838,638
Accumulated depreciation	(924,304)	(897,430)
Total real estate properties, net	2,922,930	2,941,208
Other assets, net (including receivables)	220,576	213,015
Assets held for sale, net	36,118	33,147
Liabilities of properties held for sale	201	93
Discontinued Operations
Balance Sheet data (as of the period ended):
Land	4,829	4,636
Buildings, improvements and lease intangibles	76,387	63,654
Personal property	265	82
Real estate properties, Total	81,481	68,372
Accumulated depreciation	(45,458)	(35,790)
Total real estate properties, net	36,023	32,582
Other assets, net (including receivables)	95	565
Assets held for sale, net	36,118	33,147
Accounts payable and accrued liabilities	105	38
Other liabilities	96	55
Liabilities of properties held for sale	$ 201	$ 93