XML 47 R62.htm IDEA: XBRL DOCUMENT v2.4.1.9
Allowance for Probable Loan Losses (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Allowance for probable loan losses      
Balance at the beginning of the period $ 70,161us-gaap_LoansAndLeasesReceivableAllowance $ 58,193us-gaap_LoansAndLeasesReceivableAllowance $ 84,192us-gaap_LoansAndLeasesReceivableAllowance
Losses charged to allowance (23,465)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs (14,455)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs (58,346)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
Recoveries credited to allowance 3,709us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts 3,455us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts 4,388us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
Net losses charged to allowance (19,756)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet (11,000)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet (53,958)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
Provision (credit) charged to operations 14,423us-gaap_ProvisionForLoanAndLeaseLosses 22,968us-gaap_ProvisionForLoanAndLeaseLosses 27,959us-gaap_ProvisionForLoanAndLeaseLosses
Balance at the end of the period 64,828us-gaap_LoansAndLeasesReceivableAllowance 70,161us-gaap_LoansAndLeasesReceivableAllowance 58,193us-gaap_LoansAndLeasesReceivableAllowance
Commercial      
Allowance for probable loan losses      
Balance at the beginning of the period 22,433us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
11,632us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
26,617us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
Losses charged to allowance (19,110)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
(11,737)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
(34,721)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
Recoveries credited to allowance 2,979us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
2,690us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
3,547us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
Net losses charged to allowance (16,131)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
(9,047)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
(31,174)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
Provision (credit) charged to operations 16,050us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
19,848us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
16,189us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
Balance at the end of the period 22,352us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
22,433us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
11,632us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CommercialLoanMember
Commercial real estate: other construction and land development      
Allowance for probable loan losses      
Balance at the beginning of the period 12,541us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
12,720us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
19,940us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
Losses charged to allowance (680)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
(278)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
(7,617)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
Recoveries credited to allowance 72us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
87us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
229us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
Net losses charged to allowance (608)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
(191)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
(7,388)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
Provision (credit) charged to operations 1,022us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
12us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
168us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
Balance at the end of the period 12,955us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
12,541us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
12,720us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
Risks related to family development loans      
Minimum number of family development loans 1iboc_MinimumNumberOfFamilyDevelopmentLoans
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
   
Maximum number of family development loans 4iboc_MaximumNumberOfFamilyDevelopmentLoans
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
   
Commercial real estate: farmland and commercial      
Allowance for probable loan losses      
Balance at the beginning of the period 24,467us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
21,880us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
24,227us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
Losses charged to allowance (1,893)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
(600)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
(13,724)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
Recoveries credited to allowance 107us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
152us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
220us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
Net losses charged to allowance (1,786)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
(448)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
(13,504)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
Provision (credit) charged to operations (3,998)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
3,035us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
11,157us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
Balance at the end of the period 18,683us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
24,467us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
21,880us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
Commercial real estate: multifamily      
Allowance for probable loan losses      
Balance at the beginning of the period 776us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
694us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
1,003us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
Losses charged to allowance   (5)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
 
Net losses charged to allowance   (5)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
 
Provision (credit) charged to operations 70us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
87us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
(309)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
Balance at the end of the period 846us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
776us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
694us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_CommercialRealEstateMultifamilyReceivableMember
Residential: first lien      
Allowance for probable loan losses      
Balance at the beginning of the period 3,812us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
4,390us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
4,562us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
Losses charged to allowance (351)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
(632)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
(227)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
Recoveries credited to allowance 49us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
61us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
13us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
Net losses charged to allowance (302)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
(571)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
(214)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
Provision (credit) charged to operations 79us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
(7)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
42us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
Balance at the end of the period 3,589us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
3,812us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
4,390us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialFirstMortgageFinancingReceivableMember
Residential: junior lien      
Allowance for probable loan losses      
Balance at the beginning of the period 4,249us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
4,448us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
4,760us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
Losses charged to allowance (661)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
(620)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
(1,190)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
Recoveries credited to allowance 242us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
298us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
195us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
Net losses charged to allowance (419)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
(322)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
(995)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
Provision (credit) charged to operations 853us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
123us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
683us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
Balance at the end of the period 4,683us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
4,249us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
4,448us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ResidentialSecondMortgageFinancingReceivableMember
Consumer Loan      
Allowance for probable loan losses      
Balance at the beginning of the period 750us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
1,289us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
1,724us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
Losses charged to allowance (719)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
(561)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
(756)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
Recoveries credited to allowance 210us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
162us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
184us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
Net losses charged to allowance (509)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
(399)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
(572)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
Provision (credit) charged to operations 419us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
(140)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
137us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
Balance at the end of the period 660us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
750us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
1,289us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ConsumerLoanMember
Foreign      
Allowance for probable loan losses      
Balance at the beginning of the period 1,133us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
1,140us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
1,359us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
Losses charged to allowance (51)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
(22)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
(111)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
Recoveries credited to allowance 50us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
5us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
 
Net losses charged to allowance (1)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
(17)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
(111)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
Provision (credit) charged to operations (72)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
10us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
(108)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
Balance at the end of the period $ 1,060us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
$ 1,133us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember
$ 1,140us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= iboc_ForeignReceivablesMember