INVESTMENT SECURITIES - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2024 USD ($) security	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) security	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Schedule of Investments [Line Items]
Trading securities	$ 0		$ 0
Number of available for sale investment securities | security	982		982
Number of available-for-sale securities unrealized loss position | security	973		973
Weighted average duration of MBS portfolio			5 years 8 months 12 days
Securities pledged as collateral	$ 2,900,000,000		$ 2,900,000,000		$ 3,300,000,000
Sale of investment securities available-for-sale			0	$ 0
Unamortized premiums	52,400,000		52,400,000		56,900,000
Unaccreted discounts	19,400,000		19,400,000		20,900,000
Allowance for credit losses	0		0		0
Held-to-maturity debt securities with an amortized cost basis	1,000,000,000.0		1,000,000,000.0		1,100,000,000
Accrued interest	3,600,000		3,600,000		3,700,000
Debt securities nonaccrual	0		0		0
Past due held-to-maturity debt securities	1,038,861,000		1,038,861,000		1,058,565,000
Fair value	16,800,000		16,800,000		17,400,000
Realized gain on sale of equity investments, net	2,130,000	$ 0	2,130,000	0
Other Income
Schedule of Investments [Line Items]
Gain (loss) on sale of equity investments		$ 400,000		$ 1,700,000
Past Due
Schedule of Investments [Line Items]
Past due held-to-maturity debt securities	$ 0		$ 0		$ 0