Schedule III - Real Estate and Accumulated Depreciation and Amortization - Real Estate - Held for Sale (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Gross Amount at Which Carried at Close of Period, Land, Building, Improvements & Leasehold Interests	$ 8,534,275	$ 8,448,702	$ 7,883,633	$ 7,314,132
Accumulated Depreciation and Amortization	1,319,943	$ 1,151,667	$ 1,016,271	$ 881,121
Assets Held-for-sale
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost to Company, Land	3,844
Initial Cost to Company, Building, Improvements & Leasehold Interests	4,971
Costs Capitalized Subsequent to Acquisition, Improvements	0
Costs Capitalized Subsequent to Acquisition, Carrying Costs	0
Gross Amount at Which Carried at Close of Period, Land	3,841
Gross Amount at Which Carried at Close of Period, Building, Improvements & Leasehold Interests	4,366
Gross Amount at Which Carried at Close of Period, Land, Building, Improvements & Leasehold Interests	8,207
Accumulated Depreciation and Amortization	2,536
Assets Held-for-sale | Cafe Royal [Member] | New Castle, IN 1 [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost to Company, Land	113
Initial Cost to Company, Building, Improvements & Leasehold Interests	19
Costs Capitalized Subsequent to Acquisition, Improvements	0
Costs Capitalized Subsequent to Acquisition, Carrying Costs	0
Gross Amount at Which Carried at Close of Period, Land	113
Gross Amount at Which Carried at Close of Period, Building, Improvements & Leasehold Interests	19
Gross Amount at Which Carried at Close of Period, Land, Building, Improvements & Leasehold Interests	132
Accumulated Depreciation and Amortization	$ 7
Life on Which Depreciation & Amortization in Latest Income Statement is Computed	25 years
Assets Held-for-sale | CarQuest [Member] | Bozeman, MT 1 [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost to Company, Land	28
Initial Cost to Company, Building, Improvements & Leasehold Interests	257
Costs Capitalized Subsequent to Acquisition, Improvements	0
Costs Capitalized Subsequent to Acquisition, Carrying Costs	0
Gross Amount at Which Carried at Close of Period, Land	25
Gross Amount at Which Carried at Close of Period, Building, Improvements & Leasehold Interests	257
Gross Amount at Which Carried at Close of Period, Land, Building, Improvements & Leasehold Interests	282
Accumulated Depreciation and Amortization	$ 129
Life on Which Depreciation & Amortization in Latest Income Statement is Computed	20 years
Assets Held-for-sale | SunTrust [Member] | Doral, FL 1 [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost to Company, Land	1,912
Initial Cost to Company, Building, Improvements & Leasehold Interests	1,100
Costs Capitalized Subsequent to Acquisition, Improvements	0
Costs Capitalized Subsequent to Acquisition, Carrying Costs	0
Gross Amount at Which Carried at Close of Period, Land	1,912
Gross Amount at Which Carried at Close of Period, Building, Improvements & Leasehold Interests	1,099
Gross Amount at Which Carried at Close of Period, Land, Building, Improvements & Leasehold Interests	3,011
Accumulated Depreciation and Amortization	$ 415
Life on Which Depreciation & Amortization in Latest Income Statement is Computed	20 years
Assets Held-for-sale | Vacant Property [Member] | Sacramento, CA 1 [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost to Company, Land	1,144
Initial Cost to Company, Building, Improvements & Leasehold Interests	2,961
Costs Capitalized Subsequent to Acquisition, Improvements	0
Costs Capitalized Subsequent to Acquisition, Carrying Costs	0
Gross Amount at Which Carried at Close of Period, Land	1,144
Gross Amount at Which Carried at Close of Period, Building, Improvements & Leasehold Interests	2,414
Gross Amount at Which Carried at Close of Period, Land, Building, Improvements & Leasehold Interests	3,558
Accumulated Depreciation and Amortization	$ 1,703
Life on Which Depreciation & Amortization in Latest Income Statement is Computed	40 years
Assets Held-for-sale | Vacant Property [Member] | Bay City, MI 1 [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost to Company, Land	647
Initial Cost to Company, Building, Improvements & Leasehold Interests	634
Costs Capitalized Subsequent to Acquisition, Improvements	0
Costs Capitalized Subsequent to Acquisition, Carrying Costs	0
Gross Amount at Which Carried at Close of Period, Land	647
Gross Amount at Which Carried at Close of Period, Building, Improvements & Leasehold Interests	577
Gross Amount at Which Carried at Close of Period, Land, Building, Improvements & Leasehold Interests	1,224
Accumulated Depreciation and Amortization	$ 282
Life on Which Depreciation & Amortization in Latest Income Statement is Computed	40 years