SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Allowance for loan loss	$ 20,100	$ 169,500
Accumulated deficit	$ 8,309,424	10,667,388
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Cumulative Effect, Period of Adoption, Adjustment
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Allowance for loan loss	$ 37,400
Off-balance sheet credit loss, liability	2,200
Accumulated deficit	39,600
Interest Rate Swaps
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Margin deposit assets	$ 1,600,000	$ 1,100,000