XML 18 R25.htm IDEA: XBRL DOCUMENT
v3.19.3

Investment Securities and Equity Securities with Readily Determinable Fair Values (Tables) | 9 Months Ended
--- | ---
Sep. 30, 2019
Investment Securities and Equity Securities with Readily Determinable Fair Values |
Amortized cost and estimated fair value by type of investment security | The amortized cost and estimated fair value by type of investment security at September 30, 2019 are as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Held to Maturity | ​
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | unrealized | ​ | unrealized | ​ | Estimated | ​ | Carrying | ​
​ | ​ | cost | ​ | gains | ​ | losses | ​ | fair value | ​ | value | ​
​ | ​ | (Dollars in Thousands) | ​
Other securities |  | $ | 2,400 |  | $ | — |  | $ | — |  | $ | 2,400 |  | $ | 2,400 | ​
Total investment securities | ​ | $ | 2,400 | ​ | $ | — | ​ | $ | — | ​ | $ | 2,400 | ​ | $ | 2,400 | ​
​ ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Available for Sale Debt Securities | ​
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | unrealized | ​ | unrealized | ​ | Estimated | ​ | Carrying | ​
​ | ​ | cost | ​ | gains | ​ | losses | ​ | fair value | ​ | value(1) | ​
​ | ​ | (Dollars in Thousands) | ​
Residential mortgage-backed securities |  | $ | 3,095,049 |  | $ | 19,558 |  | $ | (17,197) |  | $ | 3,097,410 |  | $ | 3,097,410 | ​
Obligations of states and political subdivisions | ​ |  | 92,199 | ​ |  | 3,263 | ​ |  | — | ​ |  | 95,462 | ​ |  | 95,462 | ​
Total investment securities | ​ | $ | 3,187,248 | ​ | $ | 22,821 | ​ | $ | (17,197) | ​ | $ | 3,192,872 | ​ | $ | 3,192,872 | ​
(1) | Included in the carrying value of residential mortgage-backed securities are $514,847 of mortgage-backed securities issued by Ginnie Mae and $2,582,563 of mortgage-backed securities issued by Fannie Mae and Freddie Mac.
​ The amortized cost and estimated fair value by type of investment security at December 31, 2018 are as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Held to Maturity | ​
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | unrealized | ​ | unrealized | ​ | Estimated | ​ | Carrying | ​
​ | ​ | cost | ​ | gains | ​ | losses | ​ | fair value | ​ | value | ​
​ | ​ | (Dollars in Thousands) | ​
Other securities |  | $ | 1,200 |  | $ | — |  | $ | — |  | $ | 1,200 |  | $ | 1,200 | ​
Total investment securities | ​ | $ | 1,200 | ​ | $ | — | ​ | $ | — | ​ | $ | 1,200 | ​ | $ | 1,200 | ​
​ ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Available for Sale | ​
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | Estimated | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | unrealized | ​ | unrealized | ​ | fair | ​ | Carrying | ​
​ | ​ | cost | ​ | gains | ​ | losses | ​ | value | ​ | value(1) | ​
​ | ​ | (Dollars in Thousands) | ​
Residential mortgage-backed securities |  | $ | 3,295,366 |  | $ | 6,813 |  | $ | (79,169) |  | $ | 3,223,010 |  | $ | 3,223,010 | ​
Obligations of states and political subdivisions | ​ |  | 185,799 | ​ |  | 2,646 | ​ |  | (105) | ​ |  | 188,340 | ​ |  | 188,340 | ​
Total investment securities | ​ | $ | 3,481,165 | ​ | $ | 9,459 | ​ | $ | (79,274) | ​ | $ | 3,411,350 | ​ | $ | 3,411,350 | ​
(1) | Included in the carrying value of residential mortgage-backed securities are $501,293 of mortgage-backed securities issued by Ginnie Mae and $2,721,717 of mortgage-backed securities issued by Fannie Mae and Freddie.
Amortized cost and fair value of investment securities, by contractual maturity | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Held to Maturity | ​ | Available for Sale | ​
​ | ​ | Amortized | ​ | Estimated | ​ | Amortized | ​ | Estimated | ​
​ | ​ | Cost | ​ | fair value | ​ | Cost | ​ | fair value | ​
​ | ​ | (Dollars in Thousands) | ​
Due in one year or less |  | $ | 1,075 |  | $ | 1,075 |  | $ | — |  | $ | — | ​
Due after one year through five years | ​ |  | 1,325 | ​ |  | 1,325 | ​ |  | — | ​ |  | — | ​
Due after five years through ten years | ​ |  | — | ​ |  | — | ​ |  | 2,243 | ​ |  | 2,267 | ​
Due after ten years | ​ |  | — | ​ |  | — | ​ |  | 89,956 | ​ |  | 93,195 | ​
Residential mortgage-backed securities | ​ |  | — | ​ |  | — | ​ |  | 3,095,049 | ​ |  | 3,097,410 | ​
Total investment securities | ​ | $ | 2,400 | ​ | $ | 2,400 | ​ | $ | 3,187,248 | ​ | $ | 3,192,872 | ​
Gross unrealized losses on investment securities and the related fair value | ​ Gross unrealized losses on debt investment securities and the fair value of the related securities, aggregated by investment category and length of time that individual debt securities have been in a continuous unrealized loss position at September 30, 2019, were as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Less than 12 months | ​ | 12 months or more | ​ | Total | ​
​ | ​ | ​ | ​ | ​ | Unrealized | ​ | ​ | ​ | ​ | Unrealized | ​ | ​ | ​ | ​ | Unrealized | ​
​ | ​ | Fair Value | ​ | Losses | ​ | Fair Value | ​ | Losses | ​ | Fair Value | ​ | Losses | ​
​ | ​ | (Dollars in Thousands) | ​
Available for sale: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Residential mortgage-backed securities |  | $ | 209,786 |  | $ | (600) |  | $ | 1,593,578 |  | $ | (16,597) |  | $ | 1,803,364 |  | $ | (17,197) | ​
​ | ​ | $ | 209,786 | ​ | $ | (600) | ​ | $ | 1,593,578 | ​ | $ | (16,597) | ​ | $ | 1,803,364 | ​ | $ | (17,197) | ​
​ Gross unrealized losses on investment securities and the fair value of the related securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at December 31, 2018 were as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Less than 12 months | ​ | 12 months or more | ​ | Total | ​
​ | ​ | ​ | ​ | ​ | Unrealized | ​ | ​ | ​ | ​ | Unrealized | ​ | ​ | ​ | ​ | Unrealized | ​
​ | ​ | Fair Value | ​ | Losses | ​ | Fair Value | ​ | Losses | ​ | Fair Value | ​ | Losses | ​
​ | ​ | (Dollars in Thousands) | ​
Available for sale: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Residential mortgage-backed securities |  | $ | 208,384 |  | $ | (2,124) |  | $ | 2,537,181 |  | $ | (77,045) |  | $ | 2,745,565 |  | $ | (79,169) | ​
Obligations of states and political subdivisions | ​ |  | 12,756 | ​ |  | (99) | ​ |  | 512 | ​ |  | (6) | ​ |  | 13,268 | ​ |  | (105) | ​
​ | ​ | $ | 221,140 | ​ | $ | (2,223) | ​ | $ | 2,537,693 | ​ | $ | (77,051) | ​ | $ | 2,758,833 | ​ | $ | (79,274) | ​
​
Summary of unrealized and realized gains and losses recognized in net income on equity securities | ​
​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended
​ | ​ | September 30, 2019
​ | ​ | (Dollars in Thousands)
​ | ​ | ​
​ | ​ | ​ | ​ | ​
Net gains recognized during the period on equity securities |  | $ | ​ | 45
Less: Net gains and (losses) recognized during the period on equity securities sold during the period | ​ |  | ​ | —
​ | ​ | ​ | ​ | ​
Unrealized gains recognized during the reporting period on equity securities still held at the reporting date | ​ | $ | ​ | 45
​
​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended
​ | ​ | September 30, 2018
​ | ​ | (Dollars in Thousands)
​ | ​ | ​
​ | ​ | ​ | ​ | ​
Net losses recognized during the period on equity securities |  | $ | ​ | (62)
Less: Net gains and (losses) recognized during the period on equity securities sold during the period | ​ |  | ​ | (771)
​ | ​ | ​ | ​ | ​
Unrealized gains recognized during the reporting period on equity securities still held at the reporting date | ​ | $ | ​ | 709
​
​ | ​ | ​ | ​ | ​
​ | ​ | Nine Months Ended
​ | ​ | September 30, 2019
​ | ​ | (Dollars in Thousands)
​ | ​ | ​
Net gains recognized during the period on equity securities |  | $ | ​ | 235
Less: Net gains and (losses) recognized during the period on equity securities sold during the period | ​ |  | ​ | —
​ | ​ | ​ | ​ | ​
Unrealized gains recognized during the reporting period on equity securities still held at the reporting date | ​ | $ | ​ | 235
​
​ | ​ | ​ | ​ | ​
​ | ​ | Nine Months Ended
​ | ​ | September 30, 2018
​ | ​ | (Dollars in Thousands)
​ | ​ | ​
Net losses recognized during the period on equity securities |  | $ | ​ | (1,083)
Less: Net gains and (losses) recognized during the period on equity securities sold during the period | ​ |  | ​ | (771)
​ | ​ | ​ | ​ | ​
Unrealized losses recognized during the reporting period on equity securities still held at the reporting date | ​ | $ | ​ | (312)

X
- Definition Tabular disclosure of realized and unrealized gains and losses in equity securities Fv-Ni. + References No definition available. + Details
Name: | iboc_EquitySecuritiesFvNiRealizedAndUnrealizedGainsLossesTableTextBlock
Namespace Prefix: | iboc_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of investment. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 325 -URI http://asc.fasb.org/topic&trid=2197064 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -URI http://asc.fasb.org/topic&trid=75115024 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -URI http://asc.fasb.org/topic&trid=2196928 Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -URI http://asc.fasb.org/topic&trid=2196965 + Details
Name: | us-gaap_InvestmentTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of maturities of an entity's investments as well as any other information pertinent to the investments. + References No definition available. + Details
Name: | us-gaap_InvestmentsClassifiedByContractualMaturityDateTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
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

X
- Definition For all investments in an unrealized loss position, including those for which other-than-temporary impairments have not been recognized in earnings (including investments for which a portion of an other-than-temporary impairment has been recognized in other comprehensive income), a tabular disclosure of the aggregate related fair value of investments with unrealized losses and the aggregate amount of unrealized losses (that is, the amount by which amortized cost basis exceeds fair value). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27290-111563 + Details
Name: | us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration