FAIR VALUE MEASUREMENTS (Narrative) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($) property	Sep. 30, 2019 USD ($) property	Dec. 31, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of properties impaired | property	11	26
Impairment of real estate assets	$ 15,983	$ 57,163
Minimum | Discount Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of real estate assets, measurement input	7.90%
Minimum | Capitalization Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of real estate assets, measurement input	7.40%
Maximum | Discount Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of real estate assets, measurement input	9.70%
Maximum | Capitalization Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of real estate assets, measurement input	9.20%
Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment	$ 859,300		$ 302,000
Real estate investment property, net, carrying value of impaired property	71,500	283,100
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment	857,900		301,600
Real estate investment property, net, carrying value of impaired property	87,500	$ 340,300
Level 2 | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument fair value disclosure	1,840,000		1,600,000
Level 2 | Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument fair value disclosure	1,850,000		$ 1,610,000
Level 2 | Broadly Syndicated Loans | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment	302,100
Level 3 | Broadly Syndicated Loans | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment	107,500
Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of CMBS	75,212
Fair value, measurements, recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of CMBS	65,491
Fair value, measurements, recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of CMBS	$ 9,721