INVESTMENT SECURITIES - Investments' Gross Unrealized Losses and Fair Value Aggregated by Investment Category and Length of Time in Continuous Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2024 USD ($) security	Dec. 31, 2023 USD ($) security
Fair Value
Less than 12 Months	$ 97,313	$ 67,007
12 Months or Longer	1,494,350	1,493,547
Total	1,591,663	1,560,554
Gross Unrealized Losses
Less than 12 Months	2,142	1,101
12 Months or Longer	245,880	219,453
Total	$ 248,022	$ 220,554
Number of Securities | security	901	865
U.S. Government-sponsored agency securities
Fair Value
Less than 12 Months	$ 0	$ 0
12 Months or Longer	93,132	95,307
Total	93,132	95,307
Gross Unrealized Losses
Less than 12 Months	0	0
12 Months or Longer	17,325	16,214
Total	$ 17,325	$ 16,214
Number of Securities | security	14	14
State and municipal
Fair Value
Less than 12 Months	$ 54,062	$ 55,514
12 Months or Longer	980,756	963,584
Total	1,034,818	1,019,098
Gross Unrealized Losses
Less than 12 Months	1,643	1,076
12 Months or Longer	134,609	115,146
Total	$ 136,252	$ 116,222
Number of Securities | security	721	691
U.S. Government-sponsored mortgage-backed securities
Fair Value
Less than 12 Months	$ 43,251	$ 11,493
12 Months or Longer	408,518	422,868
Total	451,769	434,361
Gross Unrealized Losses
Less than 12 Months	499	25
12 Months or Longer	92,970	86,965
Total	$ 93,469	$ 86,990
Number of Securities | security	156	150
Corporate obligations
Fair Value
Less than 12 Months	$ 0	$ 0
12 Months or Longer	11,944	11,788
Total	11,944	11,788
Gross Unrealized Losses
Less than 12 Months	0	0
12 Months or Longer	976	1,128
Total	$ 976	$ 1,128
Number of Securities | security	10	10