Discontinued Operations (Operating Results Relating To Assets Disposed) (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Significant Acquisitions and Disposals [Line Items]
Operating Leases, Income Statement, Lease Revenue									$ 593,022	$ 509,086	$ 441,187
Interest and Fee Income, Loans, Commercial and Residential, Real Estate									33,027	128,759	74,038
Revenues	$ 170,346	$ 169,356	$ 161,740	$ 150,527	$ 150,917	$ 160,993	$ 188,060	$ 139,951	651,969	639,921	518,320
Property operating expense									60,739	29,654	31,327
Write off of Deferred Debt Issuance Cost									38,269	31,958	1,549
Interest Expense									(142,002)	(135,870)	(133,461)
Income from discontinued operations before other items									37,241	45,036	46,093
Impairment Charges, Discontinued Operations									0	0	(8,293)
Impairment on public charter school portfolio sale									(21,433)	0	0
Gain (Loss) on Disposition of Real Estate, Discontinued Operations									31,879	0	0
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									47,687	45,036	37,800
Depreciation and amortization									158,834	138,395	121,357
Payments to Acquire Productive Assets									(500,629)	(187,460)	(397,556)
Proceeds from Sale of Real Estate									216,020	22,134	191,569
Proceeds from sale of public charter school portfolio									449,555	0	0
Payments to Acquire Mortgage Notes Receivable									(142,456)	(36,105)	(133,697)
Proceeds from mortgage note receivable paydown									217,459	335,168	21,784
Payments to Develop Real Estate Assets									(134,586)	(274,956)	(384,449)
Transfer of property under development to rental property									354,568	228,572	408,593
Noncash or Part Noncash Acquisition, Value of Assets Acquired									0	155,185	9,237
Transfer of investment in a direct financing lease to rental properties									0	0	35,807
Interest Paid, Capitalized, Investing Activities									$ 5,326	9,903	9,879
Public Charter School Portfolio Sale [Member]
Significant Acquisitions and Disposals [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]
Significant Acquisitions and Disposals [Line Items]
Operating Leases, Income Statement, Lease Revenue									36,289	47,277	43,016
Interest and Fee Income, Loans, Commercial and Residential, Real Estate									14,284	13,533	14,655
Revenues									50,573	60,810	57,671
Property operating expense									573	1,102	326
Write off of Deferred Debt Issuance Cost									181	0	0
Interest Expense									(351)	(363)	(337)
Income from discontinued operations before other items									37,241	45,036	46,093
Impairment Charges, Discontinued Operations									0	0	(8,293)
Impairment on public charter school portfolio sale									(21,433)	0	0
Gain (Loss) on Disposition of Real Estate, Discontinued Operations									31,879	0	0
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									47,687	45,036	37,800
Depreciation and amortization									12,929	15,035	11,589
Payments to Acquire Productive Assets									(6,968)	(5,956)	(28,731)
Proceeds from Sale of Real Estate									182,934	0	0
Proceeds from sale of public charter school portfolio									449,555	0	0
Payments to Acquire Mortgage Notes Receivable									(5,115)	(17,933)	(38,802)
Proceeds from mortgage note receivable paydown									28,662	3,355	12,413
Payments to Develop Real Estate Assets									(22,981)	(31,036)	(22,912)
Transfer of property under development to rental property									28,099	24,900	31,749
Noncash or Part Noncash Acquisition, Value of Assets Acquired									0	12,013	0
Transfer of investment in a direct financing lease to rental properties									0	0	35,807
Interest Paid, Capitalized, Investing Activities									$ 351	$ 363	$ 337