FAIR VALUES OF FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Carrying Amount
Assets:
Cash and cash equivalents	$ 93,684	$ 81,355
Liabilities:
Senior notes payable and other debt, gross		11,365,633
Derivative instruments	14,986	5,435
Redeemable OP Unitholder Interests	137,575	146,252
Carrying Amount | Government-Sponsored Pooled Loan Investments
Assets:
Derivative instruments	59,921	54,665
Carrying Amount | Derivative Instruments
Assets:
Derivative instruments	11,342	7,248
Carrying Amount | Secured Mortgage Loans and Other, net
Assets:
Loans receivable	466,632	1,291,694
Carrying Amount | Non-Mortgage Loan Receivable
Assets:
Loans receivable	49,972	59,857
Fair Value
Assets:
Cash and cash equivalents	93,684	81,355
Liabilities:
Senior notes payable and other debt, fair value	10,417,455	11,600,750
Derivative instruments	14,986	5,435
Redeemable OP Unitholder Interests	137,575	146,252
Fair Value | Government-Sponsored Pooled Loan Investments
Assets:
Derivative instruments	59,921	54,665
Fair Value | Derivative Instruments
Assets:
Derivative instruments	11,342	7,248
Fair Value | Secured Mortgage Loans and Other, net
Assets:
Loans receivable	445,194	1,286,322
Fair Value | Non-Mortgage Loan Receivable
Assets:
Loans receivable	$ 49,575	$ 58,849