Properties (Details) $ in Thousands, ft² in Millions	1 Months Ended		12 Months Ended					13 Months Ended	24 Months Ended
	Dec. 31, 2017 item property	Sep. 30, 2017 ft² property	Dec. 31, 2020 USD ($) property item	Dec. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($) property item	Dec. 31, 2016 ft² item	Dec. 31, 2015 item	Dec. 31, 2018 property	Dec. 31, 2018 property	Dec. 31, 2016 ft² property
Properties
Number of properties sold | property					16
Proceeds from sale of operating properties					$ 313,300
Gain on sale of property			$ 7,900	$ 59,700	55,100
Number of properties acquired by a third party which already held a non-controlling interest in the property | property				1
Amount of non-controlling interest already held by a purchaser of a property					300
Summary of properties
Properties, cost			2,573,296	$ 2,490,630
Less: accumulated depreciation			(302,143)	(224,190)
Properties, net			2,271,153	2,266,440
Future rental payments due from tenants under existing non-cancellable operating leases
2021			187,924
2022			103,617
2023			93,914
2024			85,964
2025			78,050
Thereafter			677,142
Total			1,226,611
Non-Controlling Interests
Properties
Gain on sale of property			100	5,300	$ 5,100
Property Segment
Summary of properties
Land and land improvements			484,846	484,397
Buildings and building improvements			1,690,701	1,687,756
Furniture & fixtures			$ 59,632	$ 52,567
Property Segment | Minimum
Summary of properties
Land and land improvements, useful life			0 years	0 years
Building and building improvements, useful life			5 years	5 years
Furniture & fixtures, useful life			3 years	3 years
Property Segment | Maximum
Summary of properties
Land and land improvements, useful life			15 years
Building and building improvements, useful life			45 years
Furniture & fixtures, useful life			7 years
Investing and Servicing Segment
Properties
Number of properties in portfolio investment | property			15
Total gross properties and lease intangibles			$ 269,500
Debt			$ 192,800
Number of retail properties acquired | property			0
Number of equity interests in unconsolidated commercial real estate properties | property			1
Number of industrial properties acquired | property					3
Number of properties sold | property			1	4	9
Gain on sale of property			$ 7,400	$ 59,700	$ 26,600
Number of properties acquired by a third party which already held a non-controlling interest in the property | property					1
Amount of non-controlling interest already held by a purchaser of a property					$ 300
Summary of properties
Land and land improvements			50,585	54,052
Buildings and building improvements			179,014	182,048
Furniture & fixtures			$ 2,606	$ 2,139
Investing and Servicing Segment | Minimum
Summary of properties
Land and land improvements, useful life			0 years	0 years
Building and building improvements, useful life			3 years	3 years
Furniture & fixtures, useful life			2 years	2 years
Investing and Servicing Segment | Maximum
Summary of properties
Land and land improvements, useful life			15 years
Building and building improvements, useful life			40 years
Furniture & fixtures, useful life			5 years
Investing and Servicing Segment | Non-Controlling Interests
Properties
Gain on sale of property				$ 5,300	$ 5,100
Commercial and Residential Lending Segment
Summary of properties
Land and land improvements			$ 11,416	11,386
Buildings and building improvements			19,251	$ 16,285
Construction in progress			$ 75,245
Commercial and Residential Lending Segment | Minimum
Summary of properties
Land and land improvements, useful life			0 years	0 years
Building and building improvements, useful life			10 years	10 years
Commercial and Residential Lending Segment | Maximum
Summary of properties
Land and land improvements, useful life			10 years
Building and building improvements, useful life			23 years
Ireland Portfolio
Properties
Number of properties sold | property			0	4	0
Proceeds from sale of operating properties				$ 407,200
Woodstar Portfolio
Properties
Number of properties in portfolio investment | property			32							32
Total gross properties and lease intangibles			$ 635,200
Debt			$ 572,500
Number of units acquired | item			8,948
Number of acquired properties closed | item						14	18
Woodstar II Portfolio
Properties
Number of properties in portfolio investment | property	8		27		27
Total gross properties and lease intangibles			$ 610,000
Debt			$ 437,000
Number of units acquired | property	1,740		6,109		4,369			6,109
Number of units in portfolio investment | property									27
Percentage of occupied portfolio					100.00%
Number of acquired properties closed | item	8				19
Medical Office Portfolio
Properties
Area of property | ft²						1.9				1.9
Total gross properties and lease intangibles			$ 760,200
Debt			592,400
Number of acquired properties closed | item						34
Master Lease Portfolio
Properties
Total gross properties and lease intangibles			343,800
Debt			$ 192,700
Number of retail properties acquired | property		16
Number of square feet of properties | ft²		1.9
Term of master lease agreements		24 years 7 months 6 days
Master Lease Portfolio | Disposed of by sale
Properties
Number of properties sold | property			0	0	4
Gain on sale of property					$ 28,500
REIS Equity Portfolio
Properties
Number of properties sold | property			1
Proceeds from sale of operating properties			$ 25,000	$ 145,900
Utah, Florida, Texas and Minnesota | Master Lease Portfolio | Minimum
Properties
Concentration risk (as a percent)		50.00%