SENIOR NOTES PAYABLE AND OTHER DEBT - Mortgages (Details) $ in Thousands, $ in Millions	Sep. 21, 2021 USD ($)	Sep. 30, 2021 USD ($)	Sep. 21, 2021 CAD ($)	Dec. 31, 2020 USD ($)
Business Acquisition [Line Items]
Unamortized fair value adjustment		$ 35,316		$ 12,618
Mortgages Loans and Other | New Senior Investment Group Inc. Acquisition
Business Acquisition [Line Items]
Unamortized fair value adjustment			$ 25.4
New Senior Investment Group Inc. Acquisition
Business Acquisition [Line Items]
Mortgage debt assumed in transaction	$ 482,500
New Senior Investment Group Inc. Acquisition | Mortgages Loans and Other
Business Acquisition [Line Items]
Mortgage debt assumed in transaction	$ 482,500