FAIR VALUES OF FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets:
Cash and cash equivalents	$ 143,770	$ 413,327
Escrow deposits and restricted cash	52,752	38,313
Non-mortgage loans receivable, net	63,989	57,077
Debt securities, available-for-sale, carrying value	0	237,553
Liabilities:
Long-term debt and short-term borrowings, gross	12,142,746	11,983,071
Redeemable OP Units, fair value	194,400	146,000
Non-Mortgage Loan Receivable
Assets:
Non-mortgage loans receivable, net	63,989	57,077
Non-mortgage loans receivable, fair value	64,346	57,009
Secured/mortgage loans and other, net
Assets:
Debt securities, held-to-maturity	488,999	555,840
Debt securities, held-to-maturity, fair value	477,114	508,707
Government-Sponsored Pooled Loan Investments
Assets:
Debt securities, available-for-sale, carrying value	41,440	49,727
Carrying Value
Assets:
Cash and cash equivalents	143,770	413,327
Escrow deposits and restricted cash	52,752	38,313
Derivative instruments	763	2
Liabilities:
Derivative instruments	16,286	28,338
Redeemable OP Units, carrying amount	194,424	145,983
Carrying Value | Brookdale Senior Living
Liabilities:
Warrants and Rights Outstanding	68,884	50,098
Carrying Value | Non-Mortgage Loan Receivable
Assets:
Non-mortgage loans receivable, net	63,989	57,077
Carrying Value | Secured/mortgage loans and other, net
Assets:
Debt securities, held-to-maturity	488,999	555,840
Carrying Value | Marketable debt securities
Assets:
Debt securities, available-for-sale, carrying value	0	237,553
Carrying Value | Government-Sponsored Pooled Loan Investments
Assets:
Debt securities, available-for-sale, carrying value	41,440	49,727
Fair Value
Assets:
Cash and cash equivalents, fair value	143,770	413,327
Escrow deposits and restricted cash	52,752	38,313
Derivative instruments	763	2
Liabilities:
Long-term debt and short-term borrowings, fair value	13,040,731	13,075,337
Derivative instruments	16,286	28,338
Redeemable OP Units, fair value	194,424	145,983
Fair Value | Brookdale Senior Living
Liabilities:
Warrants and Rights Outstanding	68,884	50,098
Fair Value | Non-Mortgage Loan Receivable
Assets:
Non-mortgage loans receivable, fair value	64,346	57,009
Fair Value | Secured/mortgage loans and other, net
Assets:
Debt securities, held-to-maturity, fair value	477,114	508,707
Fair Value | Marketable debt securities
Assets:
Debt securities, available-for-sale, carrying value	0	237,553
Fair Value | Government-Sponsored Pooled Loan Investments
Assets:
Debt securities, available-for-sale, carrying value	$ 41,440	$ 49,727