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SECURED AND UNSECURED DEBT, NET - Narrative (Details) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Feb. 28, 2021 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) property loan	Jun. 30, 2020 USD ($)	Jan. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jul. 31, 2020 USD ($)	Feb. 29, 2020
Secured Debt
Secured debt amount which encumbers real estate owned based upon book value		$ 1,700,000		$ 1,700,000
Percentage of secured debt which encumbers real estate owned based upon book value		12.60%		12.60%
Secured debt amount of real estate owned which is unencumbered		$ 11,900,000		$ 11,900,000
Percentage of secured debt of real estate owned which is unencumbered		87.40%		87.40%
Long-term Debt		$ 5,447,279		$ 5,447,279
Extinguishment of debt costs				40,769
Unamortized net premium		29,200		29,200			$ 12,900
300 Home Operating Community in Franklin
Secured Debt
Long-term Debt						$ 51,800
Unamortized net premium						$ 6,600
Unsecured Debt
Secured Debt
Long-term Debt		4,412,962		$ 4,412,962
Basis points added to to variable rate				90.00%
Secured Debt
Secured Debt
Long-term Debt		1,034,317		$ 1,034,317
Fixed Rate Debt
Secured Debt
Number of mortgage loans payable assumed \| loan				3
Long-term Debt		183,300		$ 183,300
Long term debt fair value		$ 201,300		$ 201,300
Number of operating properties acquired \| property				3
Fixed Rate Debt \| Mortgages Note Payable \| Minimum
Secured Debt
Notes payable maximum interest rates range		2.62%		2.62%
Fixed Rate Debt \| Mortgages Note Payable \| Maximum
Secured Debt
Notes payable maximum interest rates range		4.39%		4.39%
Fixed Rate Debt \| Unsecured Debt \| 4.00% Medium-Term Note due October 2025
Secured Debt
Repayments of outstanding borrowing	$ 300,000
Stated interest rate	4.00%	4.00%		4.00%			4.00%
Fixed Rate Debt \| Unsecured Debt \| 4.00% Medium-Term Note due October 2025 \| Interest expense
Secured Debt
Extinguishment of debt costs	$ 42,000
Fixed Rate Debt \| Unsecured Debt \| 2.95% Medium-Term Note due September 2026
Secured Debt
Long-term Debt		$ 300,000		$ 300,000			$ 300,000
Stated interest rate		2.95%		2.95%			2.95%
Portion of medium term note subject to interest rate swaps		$ 100,000		$ 100,000
All-in weighted average interest rate		2.89%		2.89%
Fixed Rate Debt \| Unsecured Debt \| 3.50 Medium-Term Note due July 2027
Secured Debt
Stated interest rate		3.50%		3.50%			3.50%
Portion of medium term note subject to interest rate swaps		$ 200,000		$ 200,000
All-in weighted average interest rate		4.03%		4.03%
Fixed Rate Debt \| Unsecured Debt \| 4.40% Medium-Term Notes due January 2029
Secured Debt
Principal outstanding								$ 300,000
Stated interest rate		4.40%		4.40%			4.40%
Portion of medium term note subject to interest rate swaps		$ 150,000		$ 150,000
All-in weighted average interest rate		4.27%		4.27%
Fixed Rate Debt \| Unsecured Debt \| 3.20% Medium-Term Notes due January 2030
Secured Debt
Stated interest rate		3.20%		3.20%			3.20%
All-in weighted average interest rate									3.32%
Fixed Rate Debt \| Unsecured Debt \| 3.00% Medium-Term Notes due August 2031
Secured Debt
Stated interest rate		3.00%		3.00%			3.00%
All-in weighted average interest rate		3.01%		3.01%
Debt		$ 150,000		$ 150,000
Fixed Rate Debt \| Unsecured Debt \| 2.10% Medium Term Note Due August 2032
Secured Debt
Stated interest rate		2.10%		2.10%
Fixed Rate Debt \| Unsecured Debt \| 2.10% Medium-Term Note due June 2033
Secured Debt
Stated interest rate	2.10%	2.10%		2.10%			2.10%
Medium-term notes	$ 300,000
Percentage of principal amount at issuance	99.592
Fixed Rate Debt \| Unsecured Debt \| 3.10% senior unsecured notes due 2034
Secured Debt
All-in weighted average interest rate		3.13%		3.13%
Fixed Rate Debt \| Unsecured Debt \| 1.90% Medium-Term Notes due March 2033
Secured Debt
Stated interest rate		1.90%		1.90%			1.90%
Fixed Rate Debt \| Secured Debt
Secured Debt
Long-term Debt		$ 1,007,317		$ 1,007,317
Fixed Rate Debt \| Secured Debt \| Mortgages Note Payable
Secured Debt
Long-term Debt		1,032,977		1,032,977			$ 835,215
Fixed Rate Debt \| Debt Assumed As Part of Acquisition \| Mortgages Note Payable
Secured Debt
Amortization of debt discount (Premium)		1,000	$ 2,500	1,700	$ 5,100
Variable Rate Debt \| Secured Debt
Secured Debt
Long-term Debt		27,000		27,000
Variable Rate Debt \| Tax-exempt secured notes payable \| Mortgages Note Payable
Secured Debt
Principal outstanding		$ 27,000		$ 27,000
Variable Rate Debt \| Tax-exempt secured notes payable \| Mortgages Note Payable
Secured Debt
Notes payable maximum interest rates range		0.73%		0.73%