Held for Sale and Discontinued Operations (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Balance Sheet data (as of the period ended):
Land	$ 201,283	$ 199,672
Buildings, improvements and lease intangibles	3,601,460	3,386,480
Personal property	10,314	10,291
Total real estate properties	3,838,638	3,628,221
Less accumulated depreciation	(897,430)	(840,839)
Total real estate properties, net	2,941,208	2,787,382
Other assets, net (including receivables)	213,015	195,666
Assets held for sale and discontinued operations, net	33,147	3,092
Liabilities of assets held for sale and discontinued operations	93	614
Discontinued Operations [Member]
Balance Sheet data (as of the period ended):
Land	4,636	1,362
Buildings, improvements and lease intangibles	63,654	4,410
Personal property	82	0
Total real estate properties	68,372	5,772
Less accumulated depreciation	(35,790)	(2,977)
Total real estate properties, net	32,582	2,795
Other assets, net (including receivables)	565	297
Assets of discontinued operations, net	565	297
Assets held for sale and discontinued operations, net	33,147	3,092
Accounts payable and accrued liabilities	38	22
Other liabilities	55	592
Liabilities of assets held for sale and discontinued operations	$ 93	$ 614