FAIR VALUES OF FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Carrying Amount
Assets:
Cash and cash equivalents	$ 92,543	$ 81,355
Liabilities:
Senior notes payable and other debt, gross	11,143,235	11,365,633
Derivative instruments	14,003	5,435
Redeemable OP Unitholder Interests	120,301	146,252
Carrying Amount | Government-Sponsored Pooled Loan Investments
Assets:
Derivative instruments	54,881	54,665
Carrying Amount | Derivative Instruments
Assets:
Derivative instruments	6,806	7,248
Carrying Amount | Secured Mortgage Loans and Other, net
Assets:
Loans receivable	1,157,638	1,291,694
Carrying Amount | Non-Mortgage Loan Receivable
Assets:
Loans receivable	56,125	59,857
Fair Value
Assets:
Cash and cash equivalents	92,543	81,355
Liabilities:
Senior notes payable and other debt, fair value	11,676,671	11,600,750
Derivative instruments	14,003	5,435
Redeemable OP Unitholder Interests	120,301	146,252
Fair Value | Government-Sponsored Pooled Loan Investments
Assets:
Derivative instruments	54,881	54,665
Fair Value | Derivative Instruments
Assets:
Derivative instruments	6,806	7,248
Fair Value | Secured Mortgage Loans and Other, net
Assets:
Loans receivable	1,158,987	1,286,322
Fair Value | Non-Mortgage Loan Receivable
Assets:
Loans receivable	$ 56,464	$ 58,849