COMMITMENTS AND CONTINGENCIES - Additional Information (Details) - USD ($) $ in Thousands	6 Months Ended	9 Months Ended
	Jun. 30, 2024	Sep. 30, 2023	Mar. 31, 2024	Jan. 01, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Line Items]
Reserves for unfunded commitments	$ 16,400				$ 18,400
Loans and Leases Receivable, Commitments, Fixed Rates	90,700	$ 108,200
Loans and Leases Receivable, Commitments, Variable Rates	$ 4,200,000	$ 4,400,000
Loan Commitments, Fixed Interest Rate Range, Minimum	0.00%	0.00%
Loan Commitments, Fixed Interest Rate Range, Maximum	21.00%	21.00%
Loan Commitments, Fixed Rate, Maturities, Minimum	1 year	1 year
Loan Commitments, Fixed Rate, Maturities, Maximum	31 years	31 years 7 months 6 days
Letters of credit issued to guarantee performance of a client to a third party	$ 33,800				34,900
Derivative, Notional Amount	19,470,720				19,339,867
Stockholders' Equity Attributable to Parent	2,326,439		$ 2,287,003		2,267,974	$ 2,143,419	$ 2,121,496	$ 2,041,373
Estimated Litigation Liability	0				0
Retained earnings
Commitments and Contingencies Disclosure [Line Items]
Stockholders' Equity Attributable to Parent	1,204,844		$ 1,166,065		1,136,718	$ 1,060,715	$ 1,016,893	$ 968,237
Cumulative Effect, Period of Adoption, Adjustment [Member]
Commitments and Contingencies Disclosure [Line Items]
Stockholders' Equity Attributable to Parent					599
Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained earnings
Commitments and Contingencies Disclosure [Line Items]
Stockholders' Equity Attributable to Parent				$ 600	599
Credit Default Swap
Commitments and Contingencies Disclosure [Line Items]
Derivative, Notional Amount	334,300				341,700
Commitments to Extend Credit
Commitments and Contingencies Disclosure [Line Items]
Commitments outstanding to extend credit	$ 4,200,000				$ 4,500,000