COMMITMENTS AND CONTINGENCIES - Allowance for Unfunded Commitments (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 01, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance, Allowance	$ 38,189	$ 208,793	$ 31,793	$ 38,189	$ 28,819	$ 28,819
Provision for unfunded commitments		26,692	5,989	132,188	14,065
Ending balance, Allowance		231,924	35,530	$ 231,924	35,530	$ 38,189	$ 28,819
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member			us-gaap:AccountingStandardsUpdate201613Member		us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201602Member
Unfunded Loan Commitments
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance, Allowance	$ 1,077	37,503	0	$ 1,077	0	$ 0
Addition due to acquisition		0	1,077	0	1,077
Provision for unfunded commitments		(10,131)	0	13,581	0
Ending balance, Allowance		27,372	1,077	27,372	1,077	1,077	$ 0
Unfunded Loan Commitments | Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance, Allowance	$ 12,714	$ 0	$ 0	$ 12,714	$ 0	0
Ending balance, Allowance						$ 12,714	$ 0