FAIR VALUE - Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets:
Investment securities available for sale	$ 1,942,568	$ 1,891,016
Held To Maturity Securities	144,815	150,627
Total gross loans held for investment portfolio	8,858,123	8,850,476	$ 8,886,873
Less: allowance for loan and lease losses	(196,362)	(231,843)	$ (205,603)	$ (240,710)
Loans held for investment, net	8,661,761	8,618,633
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Other borrowings	184,150	208,635
Carrying Reported Amount Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	586,203	716,395
Investment securities available for sale	1,942,568	1,891,016
Held To Maturity Securities	144,815	150,627
Equity Securities	44,530	43,119
Loans held for sale	43,186	32,980
Total gross loans held for investment portfolio	8,858,123	8,850,476
Less: allowance for loan and lease losses	(196,362)	(231,843)
Loans held for investment, net	8,661,761	8,618,633
Derivative Assets	1,018	312
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	8,994,714	9,022,631
Securities sold under agreements to repurchase	150,086	300,000
Advances from FHLB	740,000	715,000
Other borrowings	184,150	208,635
Derivative Liabilities	1,000	324
Estimate Of Fair Value Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	586,203	716,395
Investment securities available for sale	1,942,568	1,891,016
Held To Maturity Securities	125,658	131,032
Equity Securities	44,530	43,119
Loans held for sale	43,831	34,979
Loans held for investment, net	8,213,144	8,372,865
Derivative Assets	1,018	312
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	9,005,679	9,026,600
Securities sold under agreements to repurchase	169,366	325,913
Advances from FHLB	730,253	707,272
Other borrowings	177,201	189,424
Derivative Liabilities	1,000	324
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 1 [Member]
Assets:
Cash and due from banks and money market investments	586,203	716,395
Investment securities available for sale	7,456	7,819
Held To Maturity Securities	0	0
Equity Securities	418	0
Loans held for sale	0	0
Loans held for investment, net	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	1,917,874	1,863,342
Held To Maturity Securities	0	0
Equity Securities	44,112	43,119
Loans held for sale	27,720	25,237
Loans held for investment, net	0	0
Derivative Assets	1,018	312
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	9,005,679	9,026,600
Securities sold under agreements to repurchase	169,366	325,913
Advances from FHLB	730,253	707,272
Other borrowings	0	0
Derivative Liabilities	1,000	324
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	17,238	19,855
Held To Maturity Securities	125,658	131,032
Equity Securities	0	0
Loans held for sale	16,111	9,742
Loans held for investment, net	8,213,144	8,372,865
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	177,201	189,424
Derivative Liabilities	$ 0	$ 0