Discontinued Operations (Details) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rental revenue	$ 55,591		$ 150,962	$ 288,165	$ 438,257
Interest and Fee Income, Loans, Commercial and Residential, Real Estate	8,104		6,930	24,913	25,832
Revenues	63,877		169,356	321,249	481,623
Property operating expense	13,759		14,494	42,181	44,642
Costs associated with loan refinancing or payoff	0		38,269	820	38,269
Interest expense, net	(41,744)		(36,667)	(114,837)	(107,088)
Depreciation and amortization	42,059		41,644	128,319	116,436
Income from discontinued operations before other items	0		11,736	0	32,304
Gain (Loss) on Disposition of Real Estate, Discontinued Operations	0		13,458	0	29,948
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	$ 0		25,194	0	62,252
Payments to Acquire Mortgage Notes Receivable				(6,438)	(98,071)
Proceeds from Sale and Collection of Mortgage Notes Receivable				414	207,125
Payments to Develop Real Estate Assets				(29,963)	(125,635)
Interest cost capitalized				$ 829	5,053
Public Charter School Portfolio Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
number of properties sold		47
Proceeds from Sale of Property, Plant, and Equipment		$ 449,600
Discontinued Operations, Disposed of by Sale [Member] | Public Charter School Portfolio Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rental revenue			10,300		31,058
Interest and Fee Income, Loans, Commercial and Residential, Real Estate			5,206		12,421
Revenues			15,506		43,479
Property operating expense			169		585
Costs associated with loan refinancing or payoff			138		138
Interest expense, net			(27)		(344)
Depreciation and amortization			3,490		10,796
Income from discontinued operations before other items			11,736		32,304
Gain (Loss) on Disposition of Real Estate, Discontinued Operations			13,458		29,948
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent			$ 25,194		62,252
Payments to Acquire Productive Assets					(4,702)
Proceeds from Sale of Real Estate					165,014
Payments to Acquire Mortgage Notes Receivable					(4,966)
Proceeds from Sale and Collection of Mortgage Notes Receivable					18,419
Payments to Develop Real Estate Assets					(21,498)
Real Estate Owned, Transfer from Real Estate Owned					28,099
Interest cost capitalized					$ 344