XML 27 R73.htm IDEA: XBRL DOCUMENT
v3.19.3.a.u2

Junior Subordinated Deferrable Interest Debentures (Key Information) (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018
Junior subordinated deferrable interest debentures, major types of business trusts |  |
Junior subordinated deferrable interest debentures | $ 134,642 | $ 160,416
Trust VIII |  |
Junior subordinated deferrable interest debentures, major types of business trusts |  |
Junior subordinated deferrable interest debentures | $ 25,774 |
Interest rate (as a percent) | 5.04% |
Interest rate index | LIBOR |
Spread on interest rate index (as a percent) | 3.05% |
Trust IX |  |
Junior subordinated deferrable interest debentures, major types of business trusts |  |
Junior subordinated deferrable interest debentures | $ 41,238 |
Interest rate (as a percent) | 3.72% |
Interest rate index | LIBOR |
Spread on interest rate index (as a percent) | 1.62% |
Trust X |  |
Junior subordinated deferrable interest debentures, major types of business trusts |  |
Junior subordinated deferrable interest debentures | $ 21,021 |
Interest rate (as a percent) | 3.56% |
Interest rate index | LIBOR |
Spread on interest rate index (as a percent) | 1.65% |
Trust XI |  |
Junior subordinated deferrable interest debentures, major types of business trusts |  |
Junior subordinated deferrable interest debentures | $ 25,990 |
Interest rate (as a percent) | 3.72% |
Interest rate index | LIBOR |
Spread on interest rate index (as a percent) | 1.62% |
Trust XII |  |
Junior subordinated deferrable interest debentures, major types of business trusts |  |
Junior subordinated deferrable interest debentures | $ 20,619 |
Interest rate (as a percent) | 3.36% |
Interest rate index | LIBOR |
Spread on interest rate index (as a percent) | 1.45% |

X
- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The average effective interest rate during the reporting period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_DebtInstrumentInterestRateDuringPeriod
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Description of the interest rate as being fixed or variable, and, if variable, identification of the index or rate on which the interest rate is based and the number of points or percentage added to that index or rate to set the rate, and other pertinent information, such as frequency of rate resets. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_DebtInstrumentInterestRateTerms
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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_DebtInstrumentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Including the current and noncurrent portions, the carrying value of junior subordinated long-term debt owed to unconsolidated subsidiary trusts as of the balance sheet date. Such debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets and was initially scheduled to be repaid after one year or beyond the normal operating cycle if longer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
Name: | us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_DebtInstrumentAxis=iboc_TrustEightMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=iboc_TrustNineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=iboc_TrustTenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=iboc_TrustElevenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=iboc_TrustTwelveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |