Real Estate Investments (Summary of Assets Held-for-Sale) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charges related to properties reclassified as held for sale	$ (827)	$ (21,080)	$ (25,049)
Assets held for sale	1,176	44,519
Impaired real estate investments held for sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Land	563	6,113
Buildings, fixtures and improvements	750	39,343
Acquired intangible lease assets	0	12,517
Total real estate assets held for sale, at cost	1,313	57,973
Less accumulated depreciation and amortization	(137)	(11,278)
Total real estate investments held for sale, net	1,176	46,695
Impairment charges related to properties reclassified as held for sale	0	(2,176)
Assets held for sale	$ 1,176	$ 44,519