INVESTMENT SECURITIES - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2023 USD ($) security	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) security	Jun. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Schedule of Investments [Line Items]
Trading securities	$ 0		$ 0
Number of available for sale investment securities | security	963		963
Number of available-for-sale securities unrealized loss position | security	961		961
Weighted average duration of MBS portfolio			5 years 9 months 18 days
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	61,700,000		61,700,000		66,600,000
Unaccreted discounts	23,000,000		23,000,000		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	2,300,000		2,300,000		2,400,000
Debt securities nonaccrual	0		0		0
Past due held-to-maturity debt securities	1,079,776,000		1,079,776,000		1,111,629,000
Fair value	24,600,000		24,600,000		26,100,000
(Loss) gain on sale of equity investments	400,000	$ 6,000,000	1,700,000	6,000,000
Other Income
Schedule of Investments [Line Items]
(Loss) gain on sale of equity investments		$ (1,200,000)		$ (1,600,000)
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	$ 892,199,000		$ 892,199,000		$ 909,498,000