Period representing the term of warrant.

No definition available.

Name:	iboc_ClassOfWarrantOrRightTerm
Namespace Prefix:	iboc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the maximum amount of dividend the subsidiary banks could pay to the entity.

+ References

No definition available.

+ Details

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Namespace Prefix:	iboc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the maximum percentage of cash dividends in excess.

+ References

No definition available.

+ Details

Name:	iboc_MaximumPercentageOfCashDividendsInExcess
Namespace Prefix:	iboc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage rate used to calculate dividend payments on the preferred stock for the first five years.

+ References

No definition available.

+ Details

Name:	iboc_PreferredStockDividendRatePercentageForFirstFiveYears
Namespace Prefix:	iboc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage rate used to calculate dividend payments on the preferred stock after the first five years.

+ References

No definition available.

+ Details

Name:	iboc_PreferredStockDividendRatePercentageThereafter
Namespace Prefix:	iboc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Exercise price per share or per unit of warrants or rights outstanding.

+ References

+ Details

Name:	us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(i)(2))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph i

-Subparagraph 2

-Article 4

+ Details

Name:	us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash outflow to reacquire preferred stock during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of cash outflow in the form of ordinary dividends to preferred shareholders of the parent entity.

+ References

+ Details

Name:	us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The per share liquidation preference (or restrictions) of nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21484-112644

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph d

-Article 4

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(d)(1))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

Name:	us-gaap_PreferredStockLiquidationPreference
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Value of the difference between preference in liquidation and the par or stated values of the preferred shares.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.28)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29

-Article 5

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

+ References

+ Details

Name:	us-gaap_PreferredStockSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30

-Article 5

+ Details

Name:	us-gaap_StockRepurchasedDuringPeriodShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Capital Requirements (Details) (USD $)	0 Months Ended	12 Months Ended		48 Months Ended	0 Months Ended
Capital Requirements (Details) (USD $)	Nov. 28, 2012	Dec. 31, 2014	Dec. 31, 2012	Nov. 28, 2012	Feb. 20, 2015
Series A cumulative perpetual preferred shares, aggregate liquidation value		$ 216,000,000
Series A cumulative perpetual preferred shares, issued		216,000us-gaap_PreferredStockSharesIssued
Series A cumulative perpetual preferred shares, par value (in dollars per share)		$ 0.01
Series A cumulative perpetual preferred shares, per share liquidation value (in dollars per share)		$ 1,000
Warrants to purchase entity's common stock (in shares)		1,326,238
Warrants, exercise price (in dollars per share)		$ 24.43
Warrants, term		10 years
Senior preferred stock, dividend rate for first five years (as a percent)		5.00%
Senior preferred stock, dividend rate thereafter (as a percent)		9.00%
Senior Preferred Stock held by Treasury repurchased (in shares)	216,000
Redemption of senior preferred shares			216,000,000
Preferred stock dividends to the U.S. Treasury			10,260,000	41,520,139
Dividend payable by subsidiaries, maximum		$ 702,750,000
Subsequent Event
Warrants, exercise price (in dollars per share)					$ 24.43
Cash dividends (as a percent)					33.00%