Real Estate Investments - Discontinued Operations and Assets Held for Sale - Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Balance Sheet data (as of the period ended):
Land	$ 217,322	$ 201,283
Buildings, improvements and lease intangibles	3,669,852	3,601,460
Personal property	10,454	10,314
Real estate properties, Total	3,949,233	3,838,638
Accumulated depreciation	(989,585)	(897,430)
Total real estate properties, net	2,959,648	2,941,208
Other assets, net	222,582	213,015
Assets held for sale, net	8,826	33,147
Liabilities of properties held for sale	141	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	127	565
Assets held for sale, net	8,826	33,147
Accounts payable and accrued liabilities	119	38
Other liabilities	22	55
Liabilities of properties held for sale	$ 141	$ 93