FAIR VALUE - Carrying Amounts and Fair Values of Company's Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financial assets:
Residential mortgage loans held for sale (at fair value)	$ 44,678	$ 78,294
Investments available-for-sale	1,429,555	1,348,021
Loans, net of allowance	9,613,428	10,235,142
Accrued interest receivable	36,219	46,431
Financial liabilities:
Other deposits	10,987,400	10,033,069
Securities sold under retail repurchase agreements and federal funds purchased	147,504	543,157
Advances from FHLB	0	379,075
Subordinated debt	172,639	227,088
Carrying Amount
Financial assets:
Cash and cash equivalents	1,114,633	297,003
Residential mortgage loans held for sale (at fair value)	44,678	78,294
Investments available-for-sale	1,429,555	1,348,021
Equity securities	41,097	65,760
Loans, net of allowance	9,613,428	10,235,142
Interest rate swap agreements	6,290	9,183
Accrued interest receivable	36,219	46,431
Bank owned life insurance	146,710	126,887
Financial liabilities:
Time deposits	1,508,854	1,657,662
Other deposits	9,478,546	8,375,407
Securities sold under retail repurchase agreements and federal funds purchased	147,504	543,157
Advances from FHLB	0	379,075
Subordinated debt	172,639	227,088
Interest rate swap agreements	6,290	9,183
Accrued interest payable	3,714	3,254
Estimated Fair Value
Financial assets:
Cash and cash equivalents	1,114,633	297,003
Residential mortgage loans held for sale (at fair value)	44,678	78,294
Investments available-for-sale	1,429,555	1,348,021
Equity securities	41,097	65,760
Loans, net of allowance	9,677,624	10,336,355
Interest rate swap agreements	6,290	9,183
Accrued interest receivable	36,219	46,431
Bank owned life insurance	146,710	126,887
Financial liabilities:
Time deposits	1,515,231	1,674,112
Other deposits	9,478,546	8,375,407
Securities sold under retail repurchase agreements and federal funds purchased	147,504	543,157
Advances from FHLB	0	390,593
Subordinated debt	174,659	227,512
Interest rate swap agreements	6,290	9,183
Accrued interest payable	3,714	3,254
Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	1,114,633	297,003
Residential mortgage loans held for sale (at fair value)	0	0
Investments available-for-sale	0	0
Equity securities	41,097	65,760
Loans, net of allowance	0	0
Interest rate swap agreements	0	0
Accrued interest receivable	36,219	46,431
Bank owned life insurance	0	0
Financial liabilities:
Time deposits	0	0
Other deposits	9,478,546	8,375,407
Securities sold under retail repurchase agreements and federal funds purchased	0	0
Advances from FHLB	0	0
Subordinated debt	0	0
Interest rate swap agreements	0	0
Accrued interest payable	3,714	3,254
Significant Other Observable Inputs (Level 2) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Residential mortgage loans held for sale (at fair value)	44,678	78,294
Investments available-for-sale	1,422,146	1,338,096
Equity securities	0	0
Loans, net of allowance	0	0
Interest rate swap agreements	6,290	9,183
Accrued interest receivable	0	0
Bank owned life insurance	146,710	126,887
Financial liabilities:
Time deposits	1,515,231	1,674,112
Other deposits	0	0
Securities sold under retail repurchase agreements and federal funds purchased	147,504	543,157
Advances from FHLB	0	390,593
Subordinated debt	0	0
Interest rate swap agreements	6,290	9,183
Accrued interest payable	0	0
Significant Unobservable Inputs (Level 3) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Residential mortgage loans held for sale (at fair value)	0	0
Investments available-for-sale	7,409	9,925
Equity securities	0	0
Loans, net of allowance	9,677,624	10,336,355
Interest rate swap agreements	0	0
Accrued interest receivable	0	0
Bank owned life insurance	0	0
Financial liabilities:
Time deposits	0	0
Other deposits	0	0
Securities sold under retail repurchase agreements and federal funds purchased	0	0
Advances from FHLB	0	0
Subordinated debt	174,659	227,512
Interest rate swap agreements	0	0
Accrued interest payable	$ 0	$ 0