LOANS HELD-FOR-INVESTMENT (Allowance for Financing Receivable) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Jan. 01, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses as of December 31, 2019	$ 0
Transition adjustment on January 1, 2020	19,779,000
Provision for credit losses	17,777,000	$ 0
Allowance for credit losses as of March 31, 2020	19,779,000
Cumulative Effect, Period Of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Transition adjustment on January 1, 2020			$ 2,002,000
Mezzanine loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses as of December 31, 2019	0
Transition adjustment on January 1, 2020	14,541,000
Provision for credit losses	13,047,000
Allowance for credit losses as of March 31, 2020	14,541,000
Mezzanine loans | Cumulative Effect, Period Of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Transition adjustment on January 1, 2020			1,494,000
Senior loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses as of December 31, 2019	0
Transition adjustment on January 1, 2020	809,000
Provision for credit losses	341,000
Allowance for credit losses as of March 31, 2020	809,000
Senior loans | Cumulative Effect, Period Of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Transition adjustment on January 1, 2020			468,000
Broadly syndicated loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses as of December 31, 2019	0
Transition adjustment on January 1, 2020	4,429,000
Provision for credit losses	4,389,000
Allowance for credit losses as of March 31, 2020	$ 4,429,000
Broadly syndicated loans | Cumulative Effect, Period Of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Transition adjustment on January 1, 2020			$ 40,000