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The aggregate interest expense incurred on the following foreign deposits in domestic offices: (1) transaction accounts (NOW, and telephone and preauthorized transfer accounts), (2) money market deposits and (3) savings deposit.

No definition available.

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No definition available.

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Interest expense incurred on domestic time deposits, including certificate of deposits, of 100,000 dollars or more in domestic offices.

No definition available.

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Interest expense incurred on foreign time deposits, including certificate of deposits, of 100,000 dollars or more in domestic offices.

No definition available.

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No definition available.

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Interest expense incurred on domestic time deposits, including certificate of deposits, less than 100,000 dollars in domestic offices.

No definition available.

Name:	iboc_InterestExpenseTimeDepositsLessThan100000Domestic
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Interest expense incurred on foreign time deposits, including certificate of deposits, less than 100,000 dollars in domestic offices.

No definition available.

Name:	iboc_InterestExpenseTimeDepositsLessThan100000Foreign
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No definition available.

Name:	iboc_TimeDepositsLessThan100000Abstract
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The aggregate amount of domestic time deposits (including certificates of deposits, individual retirement accounts and open accounts) that total to less than 100,000 dollars.

No definition available.

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The aggregate amount of foreign time deposits (including certificates of deposits, individual retirement accounts and open accounts) that total to less than 100,000 dollars.

No definition available.

Name:	iboc_TimeDepositsLessThan100000Foreign
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Data Type:	xbrli:monetaryItemType
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The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

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No definition available.

Name:	us-gaap_DepositsByTypeAbstract
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The aggregate of all domestic and foreign interest-bearing deposit liabilities.

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No definition available.

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Total amount of interest-bearing domestic deposit liabilities, which may include brokered, retail, demand, checking, notice of withdrawal, money market and other interest-bearing deposits.

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Namespace Prefix:	us-gaap_
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Amount of foreign interest-bearing deposits held by the entity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 235
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-05(a))
-URI http://asc.fasb.org/extlink&oid=6882215&loc=d3e537907-122884

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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Aggregate amount of interest expense on all deposits.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.6)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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The aggregate interest expense incurred on the following for deposits in domestic offices: (1) transaction accounts (NOW, and telephone and preauthorized transfer accounts), (2) money market deposits and (3) savings deposits.

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No definition available.

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The aggregate interest expense incurred on time deposits, including certificates of deposits, in domestic offices.

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The aggregate amount of all domestic and foreign noninterest-bearing deposits liabilities held by the entity.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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No definition available.

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Amount of domestic noninterest-bearing deposits held by the entity, which may include demand deposits, checking, brokered and retail deposits.

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Amount of foreign noninterest-bearing deposits held by the entity which may include demand deposits, checking, brokered and retail deposits.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 235
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-05)
-URI http://asc.fasb.org/extlink&oid=6882215&loc=d3e537907-122884

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Amount of time deposit liabilities, including certificates of deposit.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 405
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=50488274&loc=d3e64164-112818

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Industry Guide
-Number 3
-Section V
-Paragraph D-E

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Amount of time deposit liabilities, including certificates of deposit, in denominations of $100,000 or more.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Industry Guide
-Number 3
-Section V
-Paragraph D-E