Real Estate Investments - Discontinued Operations and Assets Held for Sale - Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Balance Sheet data (as of the period ended):
Land	$ 214,755	$ 201,283
Buildings, improvements and lease intangibles	3,668,938	3,601,460
Personal property	10,355	10,314
Real estate properties, Total	3,941,783	3,838,638
Accumulated depreciation	(959,732)	(897,430)
Total real estate properties, net	2,982,051	2,941,208
Other assets, net (including receivables)	216,437	213,015
Assets held for sale, net	8,788	33,147
Liabilities of properties held for sale	340	93
Discontinued Operations
Balance Sheet data (as of the period ended):
Land	1,125	4,636
Buildings, improvements and lease intangibles	18,231	63,654
Personal property	0	82
Real estate properties, Total	19,356	68,372
Accumulated depreciation	(10,657)	(35,790)
Total real estate properties, net	8,699	32,582
Other assets, net (including receivables)	89	565
Assets held for sale, net	8,788	33,147
Accounts payable and accrued liabilities	340	38
Other liabilities	0	55
Liabilities of properties held for sale	$ 340	$ 93