Investments in Real Estate - Schedule of Net Real Estate (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Real Estate [Line Items]
Buildings and building improvements	$ 2,746,446	$ 3,476,022
Land, land estates and land improvements	341,848	456,134
Fixtures and equipment	0	84
Construction in progress	1,840	4,219
Real estate - intangible assets	419,612	599,091
Real estate, gross	3,509,746	4,535,550
Accumulated depreciation and amortization	(954,087)	(1,225,650)
Real estate, net	2,555,659	3,309,900
Accumulated amortization	231,443	334,681
Amortization expense, next 12 months	24,021
Amortization expense, year 2	21,442
Amortization expense, year 3	19,501
Amortization expense, year 4	17,448
Amortization expense, year 5	17,065
Leases, Acquired-in-Place [Member]
Real Estate [Line Items]
Real estate - intangible assets	331,607	461,624
Customer Relationships [Member]
Real Estate [Line Items]
Real estate - intangible assets	54,662	97,223
Above Market Leases [Member]
Real Estate [Line Items]
Real estate - intangible assets	$ 33,343	$ 40,244