INVESTMENT SECURITIES - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($) security	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) security	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Schedule of Investments [Line Items]
Trading securities	$ 0		$ 0
Number of available for sale investment securities | security	964		964
Number of available-for-sale securities unrealized loss position | security	964		964
Weighted average duration of MBS portfolio			6 years
Securities pledged as collateral	$ 3,300,000,000		$ 3,300,000,000		$ 2,800,000,000
Sale of investment securities available-for-sale			0	$ 0
Unamortized premiums	59,200,000		59,200,000		66,600,000
Unaccreted discounts	21,900,000		21,900,000		25,200,000
Allowance for credit losses	0		0		0
Held-to-maturity debt securities with an amortized cost basis	1,100,000,000		1,100,000,000		1,100,000,000
Accrued interest	1,700,000		1,700,000		2,400,000
Debt securities nonaccrual	0		0		0
Past due held-to-maturity debt securities	1,068,879,000		1,068,879,000		1,111,629,000
Fair value	21,700,000		21,700,000		26,100,000
Gain (loss) on sale of equity investments	700,000		(1,000,000)	6,000,000
Other Income
Schedule of Investments [Line Items]
Gain (loss) on sale of equity investments		$ 2,900,000		$ 4,500,000
Past Due
Schedule of Investments [Line Items]
Past due held-to-maturity debt securities	0		0		0
Fannie Mae (FNMA) mortgage-backed securities (MBS)
Schedule of Investments [Line Items]
Allowance for credit losses	0		0		0
Past due held-to-maturity debt securities	$ 881,844,000		$ 881,844,000		$ 909,498,000