LOANS AND ALLOWANCE FOR CREDIT LOSSES - Purchases and Sales Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Premium on loans and leases purchased	$ 4,700	$ 0	$ 2,300
Transfers to loans held for sale	0	1,139,597	376,995
Realized loss on derivatives	9,000
Gain on securitization		8,900
Multifamily \| Commercial
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transfers to loans held for sale	0	752,087	$ 81,449
Multifamily \| Federal Home Loan Mortgage Corporation \| Commercial
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transfers to loans held for sale	$ 573,900
Weighted average coupon rate (percent)	3.79%
Weighted average term to initial reset	3 years 6 months
Interest rate swaps and caps on loans
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Combined notional value		$ 543,400

Financing Receivable, Reclassification to Held-for-sale, Weighted Average Coupon

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Financing Receivable, Reclassification to Held-for-sale, Weighted Average Term to Initial Reset

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Amount of decrease in the fair value of derivatives recognized in the income statement.

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