FAIR VALUE - Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Assets:
Investment securities available for sale	$ 1,932,178	$ 2,123,525
Allowance for Credit Losse, Held-to-maturity securities	(9,268)	0
Total investment securities held to maturity, at amortized cost, net of allowance	129,266	138,675
Total gross loans held for investment portfolio	9,000
Less: allowance for loan and lease losses	(292,774)	(155,139)	$ (183,732)	$ (196,362)
Loans held for investment, net	8,746,173	8,847,066
Liabilities:
Other borrowings	184,150	184,150
Federal Reserve Bank Advances [Member]
Liabilities:
Loans payable	60,000	0
Carrying Reported Amount Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	1,087,715	644,099
Investment securities available for sale	1,932,178	2,123,525
Held to maturity securities, at amortized cost, before allowance for credit losses	138,534
Allowance for Credit Losse, Held-to-maturity securities	(9,268)
Total investment securities held to maturity, at amortized cost, net of allowance	129,266	138,675
Equity Securities	39,630	38,249
Loans held for sale	12,046	39,477
Total gross loans held for investment portfolio	9,038,947	9,002,205
Less: allowance for loan and lease losses	(292,774)	(155,139)
Loans held for investment, net	8,746,173	8,847,066
Asset Derivative	332	372
Liabilities:
Deposits	9,562,313	9,348,429
Securities sold under agreements to repurchase	300,000	100,000
Advances from FHLB	565,000	570,000
Other borrowings	184,150	184,150
Liability Derivatives	812	149
Carrying Reported Amount Fair Value Disclosure [Member] | Federal Reserve Bank Advances [Member]
Liabilities:
Loans payable	60,000
Estimate Of Fair Value Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	1,087,715	644,099
Investment securities available for sale	1,932,178	2,123,525
Total investment securities held to maturity, at amortized cost, net of allowance	111,162	110,374
Equity Securities	39,630	38,249
Loans held for sale	12,445	40,234
Loans held for investment, net	8,711,957	8,715,144
Asset Derivative	332	372
Liabilities:
Deposits	9,602,663	9,372,591
Securities sold under agreements to repurchase	331,551	120,020
Advances from FHLB	576,096	578,498
Other borrowings	156,193	180,577
Liability Derivatives	812	149
Estimate Of Fair Value Fair Value Disclosure [Member] | Federal Reserve Bank Advances [Member]
Liabilities:
Loans payable	60,000
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 1 [Member]
Assets:
Cash and due from banks and money market investments	1,087,715	644,099
Investment securities available for sale	7,582	7,479
Total investment securities held to maturity, at amortized cost, net of allowance	0	0
Equity Securities	1,458	1,428
Loans held for sale	0	0
Loans held for investment, net	0	0
Asset Derivative	0	0
Liabilities:
Deposits	0	0
Securities sold under agreements to repurchase	0	0
Advances from FHLB	0	0
Other borrowings	0	0
Liability Derivatives	0	0
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 1 [Member] | Federal Reserve Bank Advances [Member]
Liabilities:
Loans payable	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	1,910,827	2,101,456
Total investment securities held to maturity, at amortized cost, net of allowance	0	0
Equity Securities	38,172	36,821
Loans held for sale	12,445	40,234
Loans held for investment, net	0	0
Asset Derivative	332	372
Liabilities:
Deposits	9,602,663	9,372,591
Securities sold under agreements to repurchase	331,551	120,020
Advances from FHLB	576,096	578,498
Other borrowings	0	0
Liability Derivatives	812	149
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 2 [Member] | Federal Reserve Bank Advances [Member]
Liabilities:
Loans payable	60,000
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	13,769	14,590
Total investment securities held to maturity, at amortized cost, net of allowance	111,162	110,374
Equity Securities	0	0
Loans held for sale	0	0
Loans held for investment, net	8,711,957	8,715,144
Asset Derivative	0	0
Liabilities:
Deposits	0	0
Securities sold under agreements to repurchase	0	0
Advances from FHLB	0	0
Other borrowings	156,193	180,577
Liability Derivatives	0	$ 0
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 3 [Member] | Federal Reserve Bank Advances [Member]
Liabilities:
Loans payable	$ 0