XML 74 R59.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Investment Securities (Fair Value and Gross Unrealized Loss) (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2018
Available for sale: |  |
Fair value, less than 12 months |  | $ 221,140
Marketable securities, less than 12 months | $ 1,078,610 |
Unrealized losses, less than 12 Months |  | (2,223)
Marketable securities, less than 12 Months | (13,417) |
Fair value, 12 months or more |  | (2,537,693)
Marketable securities, 12 months or more | 2,037,996 |
Unrealized losses, 12 Months or More |  | (77,051)
Marketable securities, 12 Months or More | (53,050) |
Fair value, Total |  | 2,758,833
Marketable securities, Total | (3,116,606) |
Unrealized losses, Total |  | (79,274)
Marketable securities, Total | (66,467) |
Residential mortgage-backed securities |  |
Available for sale: |  |
Fair value, less than 12 months | 1,061,577 | 208,384
Unrealized losses, less than 12 Months | (13,157) | (2,124)
Fair value, 12 months or more | (2,029,455) | (2,537,181)
Unrealized losses, 12 Months or More | (52,812) | (77,045)
Fair value, Total | 3,091,032 | 2,745,565
Unrealized losses, Total | (65,969) | (79,169)
Obligations of states and political subdivisions |  |
Available for sale: |  |
Fair value, less than 12 months | 5,534 | 12,756
Unrealized losses, less than 12 Months | (9) | (99)
Fair value, 12 months or more | (522) | (512)
Unrealized losses, 12 Months or More | (7) | (6)
Fair value, Total | 6,056 | 13,268
Unrealized losses, Total | (16) | $ (105)
Equity securities with readily determinable fair values |  |
Available for sale: |  |
Equity Securities, less than 12 months | 11,499 |
Equity Securities, less than 12 Months | (251) |
Equity Securities, 12 months or more | (8,019) |
Equity Securities, 12 Months or More | (231) |
Equity Securities, Total | (19,518) |
Equity securities | $ (482) |

X
- Definition This item represents the aggregate fair value of investments in equity securities and available for sale debt securities that have been in a continuous unrealized loss position for twelve months or longer. + References No definition available. + Details
Name: | iboc_EquitySecuritiesAndAvailableForSaleDebtSecuritiesContinuousUnrealizedLossPosition12MonthsOrLonger
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investments in equity securities and available for sale debt securities that have been in a continuous loss position for twelve months or longer. + References No definition available. + Details
Name: | iboc_EquitySecuritiesAndAvailableForSaleDebtSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in equity securities and available for sale debt securities that have been in a continuous unrealized loss position for less than twelve months. + References No definition available. + Details
Name: | iboc_EquitySecuritiesAndAvailableForSaleDebtSecuritiesContinuousUnrealizedLossPositionLessThan12Months
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of accumulated unrealized loss on investments in equity securities and available for sale debt securities that have been in a continuous loss position for less than twelve months. + References No definition available. + Details
Name: | iboc_EquitySecuritiesAndAvailableForSaleDebtSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in equity securities and available for sale debt securities in an unrealized loss position. + References No definition available. + Details
Name: | iboc_EquitySecuritiesAndAvailableForSaleDebtSecuritiesUnrealizedLossPosition
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investments in equity securities and available for sale debt securities in a continuous loss position. + References No definition available. + Details
Name: | iboc_EquitySecuritiesAndAvailableForSaleDebtSecuritiesUnrealizedLossPositionAccumulatedLoss
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in equity securities that have been in a continuous unrealized loss position for twelve months or longer. + References No definition available. + Details
Name: | iboc_EquitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLonger
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investments in equity securities that have been in a continuous loss position for twelve months or longer. + References No definition available. + Details
Name: | iboc_EquitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in equity securities that have been in a continuous unrealized loss position for less than twelve months. + References No definition available. + Details
Name: | iboc_EquitySecuritiesContinuousUnrealizedLossPositionLessThan12Months
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investments in equity securities that have been in a continuous loss position for less than twelve months. + References No definition available. + Details
Name: | iboc_EquitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in equity securities in an unrealized loss position. + References No definition available. + Details
Name: | iboc_EquitySecuritiesUnrealizedLossPosition
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investments in equity securities in a continuous loss position. + References No definition available. + Details
Name: | iboc_EquitySecuritiesUnrealizedLossPositionAccumulatedLoss
Namespace Prefix: | iboc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |