LOANS HELD-FOR-INVESTMENT (Allowance for Financing Receivable) (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses as of beginning of the period	$ 27,684,000	$ 19,779,000	$ 0	$ 0
Provision for credit losses	7,355,000	7,905,000	17,777,000	33,037,000	$ 0
Allowance for credit losses end of period	35,039,000	27,684,000	19,779,000	35,039,000
Cumulative Effect, Period Of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses as of beginning of the period			2,002,000	2,002,000
Mezzanine Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses as of beginning of the period	21,269,000	14,541,000	0	0
Provision for credit losses	3,601,000	6,728,000	13,047,000
Allowance for credit losses end of period	24,870,000	21,269,000	14,541,000	24,870,000
Mezzanine Loans | Cumulative Effect, Period Of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses as of beginning of the period			1,494,000	1,494,000
Senior Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses as of beginning of the period	492,000	809,000	0	0
Provision for credit losses	1,390,000	(317,000)	341,000
Allowance for credit losses end of period	1,882,000	492,000	809,000	1,882,000
Senior Loans | Cumulative Effect, Period Of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses as of beginning of the period			468,000	468,000
Broadly Syndicated Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses as of beginning of the period	5,923,000	4,429,000	0	0
Provision for credit losses	2,364,000	1,494,000	4,389,000
Allowance for credit losses end of period	$ 8,287,000	$ 5,923,000	4,429,000	8,287,000
Broadly Syndicated Loans | Cumulative Effect, Period Of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses as of beginning of the period			$ 40,000	$ 40,000