INVESTMENT SECURITIES - Narrative (Details)	3 Months Ended
	Mar. 31, 2024 USD ($) security	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)
Schedule of Investments [Line Items]
Trading securities	$ 0
Number of available for sale investment securities | security	973
Number of available-for-sale securities unrealized loss position | security	965
Weighted average duration of MBS portfolio	5 years 9 months 18 days
Securities pledged as collateral	$ 3,000,000,000		$ 3,300,000,000
Sale of investment securities available-for-sale	0	$ 0
Unamortized premiums	54,700,000		56,900,000
Unaccreted discounts	20,300,000		20,900,000
Allowance for credit losses	0		0
Held-to-maturity debt securities with an amortized cost basis	1,000,000,000		1,000,000,000
Accrued interest	3,200,000		3,700,000
Debt securities nonaccrual	0		0
Past due held-to-maturity debt securities	1,049,815,000		1,058,565,000
Fair value	17,100,000		17,400,000
Gain (loss) on sale of equity investments	0
Other Income
Schedule of Investments [Line Items]
Gain (loss) on sale of equity investments		$ (1,300,000)
Past Due
Schedule of Investments [Line Items]
Past due held-to-maturity debt securities	0		0
Fannie Mae (FNMA) mortgage-backed securities (MBS)
Schedule of Investments [Line Items]
Allowance for credit losses	0		0
Past due held-to-maturity debt securities	$ 864,584,000		$ 872,653,000