XML 79 R64.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Allowance for Probable Loan Losses (Non-accrual Basis By Loan Class) (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Loan loss allowances, financing receivable past due |  |  |
Non-accrual loans, total | $ 54,730,000 | $ 37,245,000 | $ 47,685,000
Reduced interest income on non-accrual loans | 977,000 | 2,461,000 | $ 3,298,000
Commercial |  |  |
Loan loss allowances, financing receivable past due |  |  |
Non-accrual loans, total | 17,909,000 | 22,369,000 |
Commercial Real Estate: Other Construction and Land Development |  |  |
Loan loss allowances, financing receivable past due |  |  |
Non-accrual loans, total | 2,455,000 | 4,776,000 |
Commercial Real Estate: Farmland & Commercial |  |  |
Loan loss allowances, financing receivable past due |  |  |
Non-accrual loans, total | 33,123,000 | 8,314,000 |
Commercial Real Estate: Multifamily |  |  |
Loan loss allowances, financing receivable past due |  |  |
Non-accrual loans, total | 476,000 | 552,000 |
Residential First Lien |  |  |
Loan loss allowances, financing receivable past due |  |  |
Non-accrual loans, total | 712,000 | 655,000 |
Residential Junior Lien |  |  |
Loan loss allowances, financing receivable past due |  |  |
Non-accrual loans, total | 11,000 | 166,000 |
Consumer |  |  |
Loan loss allowances, financing receivable past due |  |  |
Non-accrual loans, total | $ 44,000 | 26,000 |
Foreign |  |  |
Loan loss allowances, financing receivable past due |  |  |
Non-accrual loans, total |  | $ 387,000 |

X
- Definition Represents the reduction in interest income on recorded investment in financing receivables that are on nonaccrual status. + References No definition available. + Details
Name: | iboc_FinancingReceivableRecordedInvestmentNonaccrualStatusReductionInInterestIncome
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524 + Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_CommercialLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=iboc_CommercialRealEstateOtherConstructionAndLandDevelopmentReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=iboc_CommercialRealEstateFarmlandAndCommercialReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=iboc_CommercialRealEstateMultifamilyReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=iboc_ResidentialFirstMortgageFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=iboc_ResidentialSecondMortgageFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_ConsumerLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=iboc_ForeignReceivablesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |