XML 51 R40.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Investment Securities and Equity Securities with Readily Determinable Fair Values (Unrealized and realized gains and losses recognized in net income on equity securities ) (Details) - USD ($) | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2018 | Jun. 30, 2018 | Dec. 31, 2017
Investment Securities and Equity Securities with Readily Determinable Fair Values |  |  |
Equity Securities | $ 27,054,000 | $ 27,054,000 | $ 27,885,000
Summary of unrealized and realized gains and losses recognized in net income on equity securities |  |  |
Net losses recognized during the period on equity securities | (247,000) | (1,021,000) |
Unrealized losses recognized during the reporting period on equity securities still held at the reporting date | $ (247,000) | $ (1,021,000) |

X
- Definition Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References No definition available. + Details
Name: | iboc_EquitySecuritiesFvNi
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition N/a + References No definition available. + Details
Name: | iboc_EquitySecuritiesFvNiGainLossAbstract
Namespace Prefix: | iboc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of realized loss from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References No definition available. + Details
Name: | iboc_EquitySecuritiesFvNiRealizedLoss
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of unrealized loss on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References No definition available. + Details
Name: | iboc_EquitySecuritiesFvNiUnrealizedLoss
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration