Discontinued Operations (Details) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rental revenue	$ 97,531	$ 147,003	$ 232,574	$ 287,295
Interest and Fee Income, Loans, Commercial and Residential, Real Estate	8,413	9,011	16,809	18,902
Revenues	106,360	161,740	257,372	312,267
Property operating expense	15,329	14,597	28,422	30,148
Interest expense, net	(38,340)	(36,458)	(73,093)	(70,421)
Depreciation and amortization	42,450	38,790	86,260	74,792
Income from discontinued operations before other items	0	10,399	0	20,568
Gain (Loss) on Disposition of Real Estate, Discontinued Operations	0	9,774	0	16,490
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	$ 0	20,173	0	37,058
Proceeds from Sale of Real Estate			3,839	95,958
Payments to Acquire Mortgage Notes Receivable			(3,667)	(33,074)
Proceeds from Sale and Collection of Mortgage Notes Receivable			94	1,954
Payments to Develop Real Estate Assets			(24,728)	(102,101)
Interest cost capitalized			$ 504	4,667
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		10,327		20,758
Interest and Fee Income, Loans, Commercial and Residential, Real Estate		3,631		7,215
Revenues		13,958		27,973
Property operating expense		174		416
Interest expense, net		(180)		(317)
Depreciation and amortization		3,565		7,306
Income from discontinued operations before other items		10,399		20,568
Gain (Loss) on Disposition of Real Estate, Discontinued Operations		9,774		16,490
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent		$ 20,173		37,058
Payments to Acquire Productive Assets				(1,827)
Proceeds from Sale of Real Estate				86,154
Payments to Acquire Mortgage Notes Receivable				(4,143)
Proceeds from Sale and Collection of Mortgage Notes Receivable				1,783
Payments to Develop Real Estate Assets				(15,041)
Real Estate Owned, Transfer from Real Estate Owned				4,748
Interest cost capitalized				$ 317