Real Estate Investments and Related Intangibles - Property Dispositions and Real Estate Assets Held for Sale (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) property	Sep. 30, 2018 USD ($) property	Sep. 30, 2019 USD ($) property joint_venture	Sep. 30, 2018 USD ($) property	Dec. 31, 2018 property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt instrument, number of properties conveyed to lender | property		1		1
Proceeds after debt assumptions and closing costs			$ 846,023	$ 358,443
Gain on disposition of real estate and real estate assets held for sale, net	$ 18,520	$ 45,295	251,106	68,451
Proceeds from disposition of discontinued operations			$ 0	123,925
Number of properties classified held for sale | property	57		57		5
Carrying value of properties classified as held for sale	$ 66,700		$ 66,700
Gain (loss) related to held for sale			$ (800)	$ (1,900)
Consolidated Property Dispositions, 2019 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties disposed | property			107
Number of consolidated properties sold | property			6
Number of joint ventures formed | joint_venture			2
Number of properties foreclosed on | property			1
Aggregate proceeds			$ 926,000
Company's share of proceeds			905,900
Proceeds after debt assumptions and closing costs			846,000
Gain on disposition of real estate and real estate assets held for sale, net			$ 251,900
Consolidated Property Dispositions, 2018 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties disposed | property				112
Aggregate proceeds				$ 371,000
Company's share of proceeds				356,600
Proceeds after debt assumptions and closing costs				352,800
Gain on disposition of real estate and real estate assets held for sale, net				$ 70,300
Red Lobster [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties disposed | property			33	22
Unconsolidated Property Dispositions, 2018 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Company's share of proceeds				$ 17,100
Number of disposed properties owned by unconsolidated joint ventures | property				1
Proceeds from disposition of discontinued operations				$ 34,100
Proceeds from after debt repayments and closing costs				5,600
Debt repayments				20,400
Net gain (loss) on sale of properties				$ 700
Industrial Partnership [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership percentage	20.00%		20.00%
Land [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Carrying value of properties classified as held for sale	$ 20,400		$ 20,400
Building Fixtures and Improvements [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Carrying value of properties classified as held for sale	$ 43,400		$ 43,400