FAIR VALUE - Financial Assets and Liabilities Accounted for at Fair Value On a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Available-for-sale investment securities
Available-for-sale investment securities	$ 5,787,158
Equity securities	465	$ 463
Derivative asset		51
U.S. Treasury and Agency Securities
Available-for-sale investment securities
Available-for-sale investment securities	4,832,087	3,998,564
Obligations of State and Political Subdivisions
Available-for-sale investment securities
Available-for-sale investment securities	476,155	430,289
Government Agency Mortgage-Backed Securities
Available-for-sale investment securities
Available-for-sale investment securities	454,247	477,056
Corporate debt securities
Available-for-sale investment securities
Available-for-sale investment securities	7,497	7,962
Government Agency Collateralized Mortgage Obligations
Available-for-sale investment securities
Available-for-sale investment securities	17,172	20,339
Significant Unobservable Inputs, Level 3
Available-for-sale investment securities
Derivative asset	7
Recurring
Available-for-sale investment securities
Available-for-sale investment securities	5,787,158	4,934,210
Equity securities	465	463
Total	5,787,750	4,935,049
Recurring | Interest Rate Swap Agreements
Available-for-sale investment securities
Derivative asset	106	296
Derivative liability		3
Recurring | ForwardContractsMember
Available-for-sale investment securities
Derivative asset	14	32
Recurring | Commitments to Originate Real Estate Loans for Sale
Available-for-sale investment securities
Derivative asset	7	51
Recurring | U.S. Treasury and Agency Securities
Available-for-sale investment securities
Available-for-sale investment securities	4,832,087	3,998,564
Recurring | Obligations of State and Political Subdivisions
Available-for-sale investment securities
Available-for-sale investment securities	476,155	430,289
Recurring | Government Agency Mortgage-Backed Securities
Available-for-sale investment securities
Available-for-sale investment securities	454,247	477,056
Recurring | Corporate debt securities
Available-for-sale investment securities
Available-for-sale investment securities	7,497	7,962
Recurring | Government Agency Collateralized Mortgage Obligations
Available-for-sale investment securities
Available-for-sale investment securities	17,172	20,339
Recurring | Quoted Prices in Active Markets For Identical Assets, Level 1
Available-for-sale investment securities
Available-for-sale investment securities	4,745,042	3,900,924
Equity securities	465	463
Total	4,745,507	3,901,387
Recurring | Quoted Prices in Active Markets For Identical Assets, Level 1 | Interest Rate Swap Agreements
Available-for-sale investment securities
Derivative asset	0	0
Derivative liability		0
Recurring | Quoted Prices in Active Markets For Identical Assets, Level 1 | ForwardContractsMember
Available-for-sale investment securities
Derivative asset	0	0
Recurring | Quoted Prices in Active Markets For Identical Assets, Level 1 | Commitments to Originate Real Estate Loans for Sale
Available-for-sale investment securities
Derivative asset	0	0
Recurring | Quoted Prices in Active Markets For Identical Assets, Level 1 | U.S. Treasury and Agency Securities
Available-for-sale investment securities
Available-for-sale investment securities	4,745,042	3,900,924
Recurring | Quoted Prices in Active Markets For Identical Assets, Level 1 | Obligations of State and Political Subdivisions
Available-for-sale investment securities
Available-for-sale investment securities	0	0
Recurring | Quoted Prices in Active Markets For Identical Assets, Level 1 | Government Agency Mortgage-Backed Securities
Available-for-sale investment securities
Available-for-sale investment securities	0	0
Recurring | Quoted Prices in Active Markets For Identical Assets, Level 1 | Corporate debt securities
Available-for-sale investment securities
Available-for-sale investment securities	0	0
Recurring | Quoted Prices in Active Markets For Identical Assets, Level 1 | Government Agency Collateralized Mortgage Obligations
Available-for-sale investment securities
Available-for-sale investment securities	0	0
Recurring | Significant Observable Inputs, Level 2
Available-for-sale investment securities
Available-for-sale investment securities	1,042,116	1,033,286
Equity securities	0	0
Total	1,042,236	1,033,611
Recurring | Significant Observable Inputs, Level 2 | Interest Rate Swap Agreements
Available-for-sale investment securities
Derivative asset	106	296
Derivative liability		3
Recurring | Significant Observable Inputs, Level 2 | ForwardContractsMember
Available-for-sale investment securities
Derivative asset	14	32
Recurring | Significant Observable Inputs, Level 2 | Commitments to Originate Real Estate Loans for Sale
Available-for-sale investment securities
Derivative asset	0	0
Recurring | Significant Observable Inputs, Level 2 | U.S. Treasury and Agency Securities
Available-for-sale investment securities
Available-for-sale investment securities	87,045	97,640
Recurring | Significant Observable Inputs, Level 2 | Obligations of State and Political Subdivisions
Available-for-sale investment securities
Available-for-sale investment securities	476,155	430,289
Recurring | Significant Observable Inputs, Level 2 | Government Agency Mortgage-Backed Securities
Available-for-sale investment securities
Available-for-sale investment securities	454,247	477,056
Recurring | Significant Observable Inputs, Level 2 | Corporate debt securities
Available-for-sale investment securities
Available-for-sale investment securities	7,497	7,962
Recurring | Significant Observable Inputs, Level 2 | Government Agency Collateralized Mortgage Obligations
Available-for-sale investment securities
Available-for-sale investment securities	17,172	20,339
Recurring | Significant Unobservable Inputs, Level 3
Available-for-sale investment securities
Available-for-sale investment securities	0	0
Equity securities	0	0
Total	7	51
Recurring | Significant Unobservable Inputs, Level 3 | Interest Rate Swap Agreements
Available-for-sale investment securities
Derivative asset	0	0
Derivative liability		0
Recurring | Significant Unobservable Inputs, Level 3 | ForwardContractsMember
Available-for-sale investment securities
Derivative asset	0	0
Recurring | Significant Unobservable Inputs, Level 3 | Commitments to Originate Real Estate Loans for Sale
Available-for-sale investment securities
Derivative asset	7	51
Recurring | Significant Unobservable Inputs, Level 3 | U.S. Treasury and Agency Securities
Available-for-sale investment securities
Available-for-sale investment securities	0	0
Recurring | Significant Unobservable Inputs, Level 3 | Obligations of State and Political Subdivisions
Available-for-sale investment securities
Available-for-sale investment securities	0	0
Recurring | Significant Unobservable Inputs, Level 3 | Government Agency Mortgage-Backed Securities
Available-for-sale investment securities
Available-for-sale investment securities	0	0
Recurring | Significant Unobservable Inputs, Level 3 | Corporate debt securities
Available-for-sale investment securities
Available-for-sale investment securities	0	0
Recurring | Significant Unobservable Inputs, Level 3 | Government Agency Collateralized Mortgage Obligations
Available-for-sale investment securities
Available-for-sale investment securities	$ 0	$ 0