INVESTMENT SECURITIES - Amortized Cost and Approximate Fair Value of Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Available for sale securities
Amortized Cost	$ 1,882,934	$ 2,273,347
Gross Unrealized Gains	0	439
Gross Unrealized Losses	382,798	297,125
Fair Value	1,500,136	1,976,661
Held to maturity securities
Amortized Cost	2,213,833	2,287,372
Allowance for Credit Losses	245	245
Net Carrying Amount	2,213,588	2,287,127
Gross Unrealized Gains	14	647
Gross Unrealized Losses	472,622	380,154
Fair Value	1,741,225	1,907,865
U.S. Treasury
Available for sale securities
Amortized Cost	1,737	2,501
Gross Unrealized Gains	0	0
Gross Unrealized Losses	24	42
Fair Value	1,713	2,459
U.S. Government-sponsored agency securities
Available for sale securities
Amortized Cost	114,414	119,154
Gross Unrealized Gains	0	0
Gross Unrealized Losses	20,829	17,192
Fair Value	93,585	101,962
Held to maturity securities
Amortized Cost	378,706	392,246
Allowance for Credit Losses	0	0
Net Carrying Amount	378,706	392,246
Gross Unrealized Gains	0	0
Gross Unrealized Losses	78,882	69,147
Fair Value	299,824	323,099
State and municipal
Available for sale securities
Amortized Cost	1,217,293	1,530,048
Gross Unrealized Gains	0	438
Gross Unrealized Losses	244,237	178,726
Fair Value	973,056	1,351,760
Held to maturity securities
Amortized Cost	1,107,325	1,117,552
Allowance for Credit Losses	245	245
Net Carrying Amount	1,107,080	1,117,307
Gross Unrealized Gains	14	647
Gross Unrealized Losses	258,536	197,064
Fair Value	848,803	921,135
U.S. Government-sponsored mortgage-backed securities
Available for sale securities
Amortized Cost	536,530	608,630
Gross Unrealized Gains	0	1
Gross Unrealized Losses	116,567	100,358
Fair Value	419,963	508,273
Held to maturity securities
Amortized Cost	726,302	776,074
Allowance for Credit Losses	0	0
Net Carrying Amount	726,302	776,074
Gross Unrealized Gains	0	0
Gross Unrealized Losses	135,163	113,915
Fair Value	591,139	662,159
Corporate obligations
Available for sale securities
Amortized Cost	12,960	13,014
Gross Unrealized Gains	0	0
Gross Unrealized Losses	1,141	807
Fair Value	11,819	12,207
Foreign investment
Held to maturity securities
Amortized Cost	1,500	1,500
Allowance for Credit Losses	0	0
Net Carrying Amount	1,500	1,500
Gross Unrealized Gains	0	0
Gross Unrealized Losses	41	28
Fair Value	$ 1,459	$ 1,472

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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