LOANS HELD-FOR-INVESTMENT (Narrative) (Details)	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) loan	Jan. 01, 2020 USD ($)	Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross sale price				$ 20,373,000
Proceeds from sale of broadly syndicated loans				19,842,000	$ 0
Gain on sale of broadly syndicated loans				223,000
Cash and cash equivalents	$ 340,939,000		$ 12,956,000	340,939,000	12,956,000	$ 473,355,000		$ 19,674,000
Transition adjustment on January 1, 2020	27,684,000	$ 19,779,000		27,684,000		0
Provision for credit losses	7,905,000	17,777,000		25,682,000	0
Provision for credit losses	7,905,000		$ 0	25,682,000	$ 0
Broadly syndicated loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value				389,200,000
Transition adjustment on January 1, 2020	5,923,000	4,429,000		5,923,000		0
Provision for credit losses	1,494,000	4,389,000
Mezzanine loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transition adjustment on January 1, 2020	21,269,000	14,541,000		21,269,000		$ 0
Provision for credit losses	6,728,000	$ 13,047,000
Number of loans | loan						8
Provision for credit losses	6,700,000
Credit Concentration Risk | Asset Benchmark | Mezzanine loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of mezzanine loans to total assets						3.80%
Unfunded Loan Commitment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other commitment	14,900,000			14,900,000
Reserves For Settlement Of Loan Acquisitions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash and cash equivalents	$ 14,300,000			$ 14,300,000
Cumulative Effect, Period Of Adoption, Adjustment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transition adjustment on January 1, 2020						$ 2,002,000	$ 2,000,000
Cumulative Effect, Period Of Adoption, Adjustment | Broadly syndicated loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transition adjustment on January 1, 2020						40,000
Cumulative Effect, Period Of Adoption, Adjustment | Mezzanine loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transition adjustment on January 1, 2020						$ 1,494,000