FAIR VALUE - Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Assets:
Investment securities available for sale	$ 1,974,226	$ 1,965,666
Less: allowance for loan and lease losses	(226,064)	(222,395)
Liabilities:
Other borrowings	231,959	231,959
Fair Value Inputs Level 3 [Member]
Assets:
Loans held for sale			54,755	[1]
Loans held for investment, net of allowance			478,393	[2]
Carrying Reported Amount Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	984,436	796,108
Investment securities available for sale	1,974,226	1,965,666
Other equity securities	26,185	25,752
Loans held for sale	81,723	76,956
Loans, held for investment	9,485,372	9,262,436
Less: allowance for loan and lease losses	(226,064)	(222,395)
Loans held for investment, net of allowance	9,259,308	9,040,041
Derivatives, included in assets	1	39
Liabilities:
Deposits	9,841,038	9,483,945
Securities sold under agreements to repurchase	900,000	900,000
Advances from FHLB	325,000	325,000
Other borrowings	231,959	231,959
Derivatives, included in liabilities	221	187
Estimate Of Fair Value Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	984,436	796,108
Investment securities available for sale	1,974,226	1,965,666
Other equity securities	26,185	25,752
Loans held for sale	82,942	77,888
Loans held for investment, net of allowance	9,115,707	8,844,659
Derivatives, included in assets	1	39
Liabilities:
Deposits	9,852,630	9,486,325
Securities sold under agreements to repurchase	966,365	958,715
Advances from FHLB	326,087	324,376
Other borrowings	169,935	162,344
Derivatives, included in liabilities	221	187
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 1 [Member]
Assets:
Cash and due from banks and money market investments	984,436	796,108
Investment securities available for sale	7,500	7,499
Other equity securities	0	0
Loans held for sale	0	0
Loans held for investment, net of allowance	0	0
Derivatives, included in assets	0	0
Liabilities:
Deposits	0	0
Securities sold under agreements to repurchase	0	0
Advances from FHLB	0	0
Other borrowings	0	0
Derivatives, included in 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	1,932,412	1,921,955
Other equity securities	26,185	25,752
Loans held for sale	28,301	23,247
Loans held for investment, net of allowance	0	0
Derivatives, included in assets	1	39
Liabilities:
Deposits	9,852,630	9,486,325
Securities sold under agreements to repurchase	966,365	958,715
Advances from FHLB	326,087	324,376
Other borrowings	0	0
Derivatives, included in liabilities	221	187
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	34,314	36,212
Other equity securities	0	0
Loans held for sale	54,641	54,641
Loans held for investment, net of allowance	9,115,707	8,844,659
Derivatives, included in assets	0	0
Liabilities:
Deposits	0	0
Securities sold under agreements to repurchase	0	0
Advances from FHLB	0	0
Other borrowings	169,935	162,344
Derivatives, included in liabilities	$ 0	$ 0

[1] The value of these loans was derived from external appraisals, adjusted for specific characteristics of the loans, and, for loans with signed sale agreements, the value was determined based on the sales price in such agreements.

[2]  Mainly impaired commercial and construction loans. The impairment was generally measured based on the fair value of the collateral. The fair values were derived from external appraisals that take into consideration prices in observed transactions involving similar assets in similar locations but adjusted for specific characteristics and assumptions of the collateral (e.g. absorption rates), which are not market observable.