FAIR VALUE - Fair Value (Detail) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Assets:
Investment securities available for sale		$ 1,904,255	$ 1,886,395
Less: allowance for loan and lease losses		(238,125)	(240,710)
Liabilities:
Other borrowings		216,183	226,492
Fair Value Inputs Level 3 [Member]
Assets:
Loans held for sale	[1]			$ 54,588
Loans held for investment, net of allowance	[2]			$ 436,944
Carrying Reported Amount Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments		1,026,825	752,458
Investment securities available for sale		1,904,255	1,886,395
Other equity securities		32,310	32,169
Loans held for sale		37,868	35,869
Loans, held for investment		9,131,342	9,273,865
Less: allowance for loan and lease losses		(238,125)	(240,710)
Loans held for investment, net of allowance		8,893,217	9,033,155
Derivatives, included in assets		368	806
Liabilities:
Deposits		9,434,780	9,338,124
Securities sold under agreements to repurchase		700,000	700,000
Advances from FHLB		455,000	455,000
Other borrowings		216,183	226,492
Derivatives, included in liabilities		636	921
Estimate Of Fair Value Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments		1,026,825	752,458
Investment securities available for sale		1,904,255	1,886,395
Other equity securities		32,310	32,169
Loans held for sale		41,138	36,844
Loans held for investment, net of allowance		8,855,624	8,899,696
Derivatives, included in assets		368	806
Liabilities:
Deposits		9,451,510	9,334,073
Securities sold under agreements to repurchase		721,312	752,048
Advances from FHLB		456,895	453,182
Other borrowings		159,598	142,846
Derivatives, included in liabilities		636	921
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 1 [Member]
Assets:
Cash and due from banks and money market investments		1,026,825	752,458
Investment securities available for sale		7,932	7,497
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		1,869,660	1,851,601
Other equity securities		32,310	32,169
Loans held for sale		30,718	28,709
Loans held for investment, net of allowance		0	0
Derivatives, included in assets		368	806
Liabilities:
Deposits		9,451,510	9,334,073
Securities sold under agreements to repurchase		721,312	752,048
Advances from FHLB		456,895	453,182
Other borrowings		0	0
Derivatives, included in liabilities		636	921
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		26,663	27,297
Other equity securities		0	0
Loans held for sale		10,420	8,135
Loans held for investment, net of allowance		8,855,624	8,899,696
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		159,598	142,846
Derivatives, included in liabilities		$ 0	$ 0

[1] The value of these loans was derived from external appraisals, adjusted for specific characteristics of the loans.

[2] Consist mainly of impaired commercial and construction loans. The impairment was generally measured based on the fair value of the collateral. The fair value was 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.