FAIR VALUES OF FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets:
Cash and cash equivalents	$ 992,824	$ 106,363
Escrow deposits and restricted cash	36,312	39,739
Non-mortgage loans receivable, net	16,146	63,724
Debt securities, available-for-sale, carrying value	220,630	237,360
Liabilities:
Long-term debt and short-term borrowings, gross	12,628,317	12,245,802
Redeemable OP Units, fair value	119,200	171,200
Non-Mortgage Loan Receivable
Assets:
Non-mortgage loans receivable, net	16,146	63,724
Non-mortgage loans receivable, fair value	15,007	63,538
Secured/mortgage loans and other, net
Assets:
Debt securities, held-to-maturity	633,582	645,546
Debt securities, held-to-maturity, fair value	529,374	646,925
Government-Sponsored Pooled Loan Investments
Assets:
Debt securities, available-for-sale, carrying value	48,249	59,066
Carrying Value
Assets:
Cash and cash equivalents	992,824	106,363
Escrow deposits and restricted cash	36,312	39,739
Derivative instruments	707	738
Liabilities:
Derivative instruments	31,962	12,987
Redeemable OP Units, carrying amount	119,233	171,178
Carrying Value | Non-Mortgage Loan Receivable
Assets:
Non-mortgage loans receivable, net	16,146	63,724
Carrying Value | Secured/mortgage loans and other, net
Assets:
Debt securities, held-to-maturity	633,582	645,546
Carrying Value | Marketable debt securities
Assets:
Debt securities, available-for-sale, carrying value	220,630	237,360
Carrying Value | Government-Sponsored Pooled Loan Investments
Assets:
Debt securities, available-for-sale, carrying value	48,249	59,066
Fair Value
Assets:
Cash and cash equivalents, fair value	992,824	106,363
Escrow deposits and restricted cash	36,312	39,739
Derivative instruments	707	738
Liabilities:
Long-term debt and short-term borrowings, fair value	13,095,984	12,778,758
Derivative instruments	31,962	12,987
Redeemable OP Units, fair value	119,233	171,178
Fair Value | Non-Mortgage Loan Receivable
Assets:
Non-mortgage loans receivable, fair value	15,007	63,538
Fair Value | Secured/mortgage loans and other, net
Assets:
Debt securities, held-to-maturity, fair value	529,374	646,925
Fair Value | Marketable debt securities
Assets:
Debt securities, available-for-sale, carrying value	220,630	237,360
Fair Value | Government-Sponsored Pooled Loan Investments
Assets:
Debt securities, available-for-sale, carrying value	$ 48,249	$ 59,066