XML 19 R37.htm IDEA: XBRL DOCUMENT v2.4.1.9
Allowance for Probable Loan Losses (Details 6) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Loan portfolio by credit quality indicator    
Portfolio, total $ 5,778,742us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome $ 5,679,245us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
Pass    
Loan portfolio by credit quality indicator    
Portfolio, total 5,438,270us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 5,328,410us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Special Review    
Loan portfolio by credit quality indicator    
Portfolio, total 54,443us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 54,561us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Watch List - Pass    
Loan portfolio by credit quality indicator    
Portfolio, total 35,189us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= iboc_SpecialPassMember		 37,674us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= iboc_SpecialPassMember
Watch List - Substandard    
Loan portfolio by credit quality indicator    
Portfolio, total 177,090us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 182,429us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Watch List - Impaired    
Loan portfolio by credit quality indicator    
Portfolio, total 73,750us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember		 76,171us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember
Commercial    
Loan portfolio by credit quality indicator    
Portfolio, total 1,093,283us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember		 1,089,486us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
Commercial | Pass    
Loan portfolio by credit quality indicator    
Portfolio, total 967,008us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 961,490us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Commercial | Special Review    
Loan portfolio by credit quality indicator    
Portfolio, total 38,461us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 38,382us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Commercial | Watch List - Pass    
Loan portfolio by credit quality indicator    
Portfolio, total 4,505us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= iboc_SpecialPassMember		 3,793us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= iboc_SpecialPassMember
Commercial | Watch List - Substandard    
Loan portfolio by credit quality indicator    
Portfolio, total 42,054us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 45,646us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Commercial | Watch List - Impaired    
Loan portfolio by credit quality indicator    
Portfolio, total 41,255us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember		 40,175us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember
Commercial real estate: other construction and land development    
Loan portfolio by credit quality indicator    
Portfolio, total 1,522,571us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember		 1,414,977us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
Commercial real estate: other construction and land development | Pass    
Loan portfolio by credit quality indicator    
Portfolio, total 1,462,611us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 1,353,971us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Commercial real estate: other construction and land development | Special Review    
Loan portfolio by credit quality indicator    
Portfolio, total 993us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 1,005us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Commercial real estate: other construction and land development | Watch List - Pass    
Loan portfolio by credit quality indicator    
Portfolio, total 10,421us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= iboc_SpecialPassMember		 10,428us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= iboc_SpecialPassMember
Commercial real estate: other construction and land development | Watch List - Substandard    
Loan portfolio by credit quality indicator    
Portfolio, total 38,614us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 38,697us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Commercial real estate: other construction and land development | Watch List - Impaired    
Loan portfolio by credit quality indicator    
Portfolio, total 9,932us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember		 10,876us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember
Commercial real estate: farmland and commercial    
Loan portfolio by credit quality indicator    
Portfolio, total 1,895,993us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember		 1,901,399us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
Commercial real estate: farmland and commercial | Pass    
Loan portfolio by credit quality indicator    
Portfolio, total 1,754,758us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 1,754,741us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Commercial real estate: farmland and commercial | Special Review    
Loan portfolio by credit quality indicator    
Portfolio, total 11,502us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 11,674us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Commercial real estate: farmland and commercial | Watch List - Pass    
Loan portfolio by credit quality indicator    
Portfolio, total 20,263us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= iboc_SpecialPassMember		 23,453us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= iboc_SpecialPassMember
Commercial real estate: farmland and commercial | Watch List - Substandard    
Loan portfolio by credit quality indicator    
Portfolio, total 96,003us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 97,365us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Commercial real estate: farmland and commercial | Watch List - Impaired    
Loan portfolio by credit quality indicator    
Portfolio, total 13,467us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember		 14,166us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember
Commercial real estate: multifamily    
Loan portfolio by credit quality indicator    
Portfolio, total 105,246us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember		 116,699us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
Commercial real estate: multifamily | Pass    
Loan portfolio by credit quality indicator    
Portfolio, total 104,270us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 115,729us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Commercial real estate: multifamily | Watch List - Substandard    
Loan portfolio by credit quality indicator    
Portfolio, total 135us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 135us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Commercial real estate: multifamily | Watch List - Impaired    
Loan portfolio by credit quality indicator    
Portfolio, total 841us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember		 835us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember
Residential: first lien    
Loan portfolio by credit quality indicator    
Portfolio, total 423,808us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember		 422,026us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
Residential: first lien | Pass    
Loan portfolio by credit quality indicator    
Portfolio, total 415,011us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 412,668us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Residential: first lien | Special Review    
Loan portfolio by credit quality indicator    
Portfolio, total 3,487us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 3,500us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Residential: first lien | Watch List - Substandard    
Loan portfolio by credit quality indicator    
Portfolio, total 17us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 18us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Residential: first lien | Watch List - Impaired    
Loan portfolio by credit quality indicator    
Portfolio, total 5,293us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember		 5,840us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember
Residential: junior lien    
Loan portfolio by credit quality indicator    
Portfolio, total 493,130us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember		 488,300us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
Residential: junior lien | Pass    
Loan portfolio by credit quality indicator    
Portfolio, total 491,494us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 484,968us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Residential: junior lien | Watch List - Substandard    
Loan portfolio by credit quality indicator    
Portfolio, total 267us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 437us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Residential: junior lien | Watch List - Impaired    
Loan portfolio by credit quality indicator    
Portfolio, total 1,369us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember		 2,895us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember
Consumer Loan    
Loan portfolio by credit quality indicator    
Portfolio, total 59,254us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember		 61,137us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
Consumer Loan | Pass    
Loan portfolio by credit quality indicator    
Portfolio, total 58,066us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 59,622us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Consumer Loan | Watch List - Substandard    
Loan portfolio by credit quality indicator    
Portfolio, total   131us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Consumer Loan | Watch List - Impaired    
Loan portfolio by credit quality indicator    
Portfolio, total 1,188us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember		 1,384us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember
Foreign    
Loan portfolio by credit quality indicator    
Portfolio, total 185,457us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember		 185,221us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
Foreign | Pass    
Loan portfolio by credit quality indicator    
Portfolio, total 185,052us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 185,221us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Foreign | Watch List - Impaired    
Loan portfolio by credit quality indicator    
Portfolio, total $ 405us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember