FAIR VALUE (Carrying Amounts and Fair Values of Company's Financial Instruments) (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial assets:
Residential mortgage loans held for sale (at fair value)	$ 88,728	$ 53,701
Investments available-for-sale (at fair value)	1,357,205	1,073,333
Loans, net of allowance	10,163,621	6,649,100
Accrued interest receivable	48,176	23,282
Financial liabilities:
Other deposits	9,964,969	6,440,319
Securities sold under retail repurchase agreements and federal funds purchased	462,706	213,605
Advances from FHLB	444,210	513,777
Subordinated debt	230,300	209,406
Carrying Amount
Financial assets:
Cash and cash equivalents	224,883	146,103
Residential mortgage loans held for sale (at fair value)	88,728	53,701
Investments available-for-sale (at fair value)	1,357,205	1,073,333
Equity securities	68,528	51,803
Loans, net of allowance	10,163,621	6,649,100
Interest rate swap agreements	10,223	2,507
Accrued interest receivable	48,176	23,282
Bank owned life insurance	126,182	113,171
Financial liabilities:
Time Deposits	1,868,285	1,542,322
Other deposits	8,096,684	4,897,997
Securities sold under retail repurchase agreements and federal funds purchased	462,706	213,605
Advances from FHLB	444,210	513,777
Subordinated debt	230,300	209,406
Interest rate swap agreements	10,223	2,507
Accrued interest payable	6,822	4,194
Estimated Fair Value
Financial assets:
Cash and cash equivalents	224,883	146,103
Residential mortgage loans held for sale (at fair value)	88,728	53,701
Investments available-for-sale (at fair value)	1,357,205	1,073,333
Equity securities	68,528	51,803
Loans, net of allowance	10,332,039	6,628,054
Interest rate swap agreements	10,223	2,507
Accrued interest receivable	48,176	23,282
Bank owned life insurance	126,182	113,171
Financial liabilities:
Time Deposits	1,889,807	1,547,116
Other deposits	8,096,684	4,897,997
Securities sold under retail repurchase agreements and federal funds purchased	462,889	213,605
Advances from FHLB	457,875	520,729
Subordinated debt	234,808	200,864
Interest rate swap agreements	10,223	2,507
Accrued interest payable	6,822	4,194
Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	224,883	146,103
Residential mortgage loans held for sale (at fair value)	0	0
Investments available-for-sale (at fair value)	0	0
Equity securities	68,528	51,803
Loans, net of allowance	0	0
Interest rate swap agreements	0	0
Accrued interest receivable	48,176	23,282
Bank owned life insurance	0	0
Financial liabilities:
Time Deposits	0	0
Other deposits	8,096,684	4,897,997
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	6,822	4,194
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)	88,728	53,701
Investments available-for-sale (at fair value)	1,344,706	1,063,471
Equity securities	0	0
Loans, net of allowance	0	0
Interest rate swap agreements	10,223	2,507
Accrued interest receivable	0	0
Bank owned life insurance	126,182	113,171
Financial liabilities:
Time Deposits	1,889,807	1,547,116
Other deposits	0	0
Securities sold under retail repurchase agreements and federal funds purchased	462,889	213,605
Advances from FHLB	457,875	520,729
Subordinated debt	0	0
Interest rate swap agreements	10,223	2,507
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 (at fair value)	12,499	9,862
Equity securities	0	0
Loans, net of allowance	10,332,039	6,628,054
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	234,808	200,864
Interest rate swap agreements	0	0
Accrued interest payable	$ 0	$ 0