INVESTMENT SECURITIES - Amortized Cost and Approximate Fair Value of Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Available for sale securities
Amortized Cost	$ 2,039,927	$ 2,273,347
Gross Unrealized Gains	567	439
Gross Unrealized Losses	246,286	297,125
Fair Value	1,794,208	1,976,661
Held to maturity securities
Amortized Cost	2,263,426	2,287,372
Allowance for Credit Losses	245	245
Net Carrying Amount	2,263,181	2,287,127
Gross Unrealized Gains	1,778	647
Gross Unrealized Losses	330,603	380,154
Fair Value	1,934,601	1,907,865
U.S. Treasury
Available for sale securities
Amortized Cost	2,114	2,501
Gross Unrealized Gains	0	0
Gross Unrealized Losses	32	42
Fair Value	2,082	2,459
U.S. Government-sponsored agency securities
Available for sale securities
Amortized Cost	117,746	119,154
Gross Unrealized Gains	5	0
Gross Unrealized Losses	15,153	17,192
Fair Value	102,598	101,962
Held to maturity securities
Amortized Cost	388,273	392,246
Allowance for Credit Losses	0	0
Net Carrying Amount	388,273	392,246
Gross Unrealized Gains	0	0
Gross Unrealized Losses	61,813	69,147
Fair Value	326,460	323,099
State and municipal
Available for sale securities
Amortized Cost	1,322,500	1,530,048
Gross Unrealized Gains	562	438
Gross Unrealized Losses	139,326	178,726
Fair Value	1,183,736	1,351,760
Held to maturity securities
Amortized Cost	1,114,874	1,117,552
Allowance for Credit Losses	245	245
Net Carrying Amount	1,114,629	1,117,307
Gross Unrealized Gains	1,778	647
Gross Unrealized Losses	166,679	197,064
Fair Value	949,973	921,135
U.S. Government-sponsored mortgage-backed securities
Available for sale securities
Amortized Cost	584,576	608,630
Gross Unrealized Gains	0	1
Gross Unrealized Losses	90,971	100,358
Fair Value	493,605	508,273
Held to maturity securities
Amortized Cost	758,779	776,074
Allowance for Credit Losses	0	0
Net Carrying Amount	758,779	776,074
Gross Unrealized Gains	0	0
Gross Unrealized Losses	102,068	113,915
Fair Value	656,711	662,159
Corporate obligations
Available for sale securities
Amortized Cost	12,991	13,014
Gross Unrealized Gains	0	0
Gross Unrealized Losses	804	807
Fair Value	12,187	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	43	28
Fair Value	$ 1,457	$ 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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