FAIR VALUE - Fair Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2017		Dec. 31, 2016	Jun. 30, 2016	[2]
Assets:
Investment securities available for sale	$ 1,750,472		$ 1,881,920
Held To Maturity Securities	150,627		156,190
Less: allowance for loan and lease losses	(230,870)		(205,603)
Derivatives, included in assets	294		554
Liabilities:
Other borrowings	208,639		216,187
Derivatives, included in liabilities	221		753
Fair Value Inputs Level 1 [Member]
Assets:
Loans held for investment, net of allowance	0	[1]		$ 0
Fair Value Inputs Level 2 [Member]
Assets:
Loans held for investment, net of allowance	0	[1]		0
Fair Value Inputs Level 3 [Member]
Assets:
Loans held for investment, net of allowance	374,740	[1]		$ 426,444
Carrying Reported Amount Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	737,194		299,685
Investment securities available for sale	1,750,472		1,881,920
Held To Maturity Securities	150,627		156,190
Other equity securities	52,119		42,992
Loans held for sale	27,576		50,006
Loans, held for investment	8,877,214		8,886,873
Less: allowance for loan and lease losses	(230,870)		(205,603)
Loans held for investment, net of allowance	8,646,344		8,681,270
Derivatives, included in assets	294		554
Liabilities:
Deposits	8,765,891		8,831,205
Securities sold under agreements to repurchase	300,000		300,000
Advances from FHLB	915,000		670,000
Other borrowings	208,639		216,187
Derivatives, included in liabilities	221		753
Estimate Of Fair Value Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	737,194		299,685
Investment securities available for sale	1,750,472		1,881,920
Held To Maturity Securities	130,125		132,759
Other equity securities	52,119		42,992
Loans held for sale	29,612		52,707
Loans held for investment, net of allowance	8,354,635		8,455,104
Derivatives, included in assets	294		554
Liabilities:
Deposits	8,769,746		8,838,606
Securities sold under agreements to repurchase	329,444		335,840
Advances from FHLB	913,134		669,687
Other borrowings	180,305		171,374
Derivatives, included in liabilities	221		753
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 1 [Member]
Assets:
Cash and due from banks and money market investments	737,194		299,685
Investment securities available for sale	7,850		7,917
Held To Maturity Securities	0		0
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	1,722,283		1,851,089
Held To Maturity Securities	0		0
Other equity securities	52,119		42,992
Loans held for sale	19,826		42,921
Loans held for investment, net of allowance	0		0
Derivatives, included in assets	294		554
Liabilities:
Deposits	8,769,746		8,838,606
Securities sold under agreements to repurchase	329,444		335,840
Advances from FHLB	913,134		669,687
Other borrowings	0		0
Derivatives, included in liabilities	221		753
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	20,339		22,914
Held To Maturity Securities	130,125		132,759
Other equity securities	0		0
Loans held for sale	9,786		9,786
Loans held for investment, net of allowance	8,354,635		8,455,104
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	180,305		171,374
Derivatives, included in liabilities	$ 0		$ 0

[1] Consist mainly of impaired commercial and construction loans. The impairments were generally measured based on the fair value of underlying 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.

[2] Consist mainly of impaired commercial and construction loans. The impairments were generally measured based on the fair value of the underlying 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.