FAIR VALUE - Carrying amounts and estimated fair values of other financial instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Financial assets:
Held-to-maturity securities	$ 1,034,795	$ 0
Financial liabilities:
Overnight borrowings	768,400	0
Carrying Value
Financial assets:
Net loans	8,748,335	7,323,770
Held-to-maturity securities	1,079,695	0
Financial liabilities:
Deposits	13,012,308	12,911,168
Overnight borrowings	768,400	0
Securities sold under agreement to repurchase, short-term	346,652	324,720
Other Federal Home Loan Bank borrowings	19,474	1,888
Subordinated notes payable	3,249	3,277
Fair Value
Financial assets:
Net loans	8,696,185	7,523,024
Held-to-maturity securities	1,034,795	0
Financial liabilities:
Deposits	12,981,487	12,911,197
Overnight borrowings	768,400	0
Securities sold under agreement to repurchase, short-term	346,652	324,720
Other Federal Home Loan Bank borrowings	19,377	1,907
Subordinated notes payable	$ 3,249	$ 3,277