FAIR VALUE - Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets:
Investment securities available for sale	$ 4,647,019	$ 2,123,525
Less: allowance for credit losses on held to maturity securities	(8,845)	0
Held To Maturity Securities Net Of Allowance For Credit Losses	180,643	138,675
Less: allowance for loan and lease losses	(385,887)	(155,139)	$ (196,362)	$ (231,843)
Loans, net of allowance for credit losses	11,391,402	8,847,066
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Other borrowings	183,762	184,150
Carrying Reported Amount Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	1,493,833	644,099
Investment securities available for sale	4,647,019	2,123,525
Held To Maturity Securities Amortized	189,488	138,675
Less: allowance for credit losses on held to maturity securities	(8,845)
Held To Maturity Securities Net Of Allowance For Credit Losses	180,643
Equity Securities	37,588	38,249
Loans held for sale	50,289	39,477
Total gross loans held for investment portfolio	11,777,289	9,002,205
Less: allowance for loan and lease losses	(385,887)
Loans, net of allowance for credit losses	11,391,402	8,847,066
Derivative Assets	2,482	372
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	15,317,383	9,348,429
Securities sold under agreements to repurchase	300,000	100,000
Advances from FHLB	440,000	570,000
Other borrowings	183,762	184,150
Derivative Liabilities	1,920	149
Estimate Of Fair Value Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	1,493,833	644,099
Investment securities available for sale	4,647,019	2,123,525
Held To Maturity Securities Amortized		110,374
Held To Maturity Securities Net Of Allowance For Credit Losses	173,806
Equity Securities	37,588	38,249
Loans held for sale	52,322	40,234
Loans, net of allowance for credit losses	11,564,635	8,715,144
Derivative Assets	2,482	372
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	15,363,236	9,372,591
Securities sold under agreements to repurchase	329,493	120,020
Advances from FHLB	446,703	578,498
Other borrowings	151,645	180,577
Derivative Liabilities	1,920	149
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 1 [Member]
Assets:
Cash and due from banks and money market investments	1,493,833	644,099
Investment securities available for sale	7,507	7,479
Held To Maturity Securities Amortized		0
Held To Maturity Securities Net Of Allowance For Credit Losses	0
Equity Securities	1,474	1,428
Loans held for sale	0	0
Loans, net of allowance for credit losses	0	0
Derivative Assets	0	0
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	0	0
Securities sold under agreements to repurchase	0	0
Advances from FHLB	0	0
Other borrowings	0	0
Derivative Liabilities	0	0
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 2 [Member]
Assets:
Cash and due from banks and money market investments	0	0
Investment securities available for sale	4,627,535	2,101,456
Held To Maturity Securities Amortized		0
Held To Maturity Securities Net Of Allowance For Credit Losses	0
Equity Securities	36,114	36,821
Loans held for sale	52,322	40,234
Loans, net of allowance for credit losses	0	0
Derivative Assets	2,482	372
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	15,363,236	9,372,591
Securities sold under agreements to repurchase	329,493	120,020
Advances from FHLB	446,703	578,498
Other borrowings	0	0
Derivative Liabilities	1,920	149
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 3 [Member]
Assets:
Cash and due from banks and money market investments	0	0
Investment securities available for sale	11,977	14,590
Held To Maturity Securities Amortized		110,374
Held To Maturity Securities Net Of Allowance For Credit Losses	173,806
Equity Securities	0	0
Loans held for sale	0	0
Loans, net of allowance for credit losses	11,564,635	8,715,144
Derivative Assets	0	0
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	0	0
Securities sold under agreements to repurchase	0	0
Advances from FHLB	0	0
Other borrowings	151,645	180,577
Derivative Liabilities	$ 0	$ 0