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Borrowed Funds (Narrative) (Detail) $ in Thousands |  | 12 Months Ended
--- | --- | ---
Mar. 17, 2017 USD ($) | Dec. 31, 2024 USD ($) quarter | Dec. 31, 2023 USD ($) | Dec. 31, 2004 USD ($)
Borrowed Funds [Line Items] |  |  |  |
Federal funds purchased |  | $ 21,975 | $ 14,200 |
Repurchase agreements |  | 4,342,941 | 4,127,188 |
Subordinated notes |  | 99,648 | 99,491 |
Junior subordinated deferrable interest debentures |  | $ 123,184 | 123,127 |
Maximum number of quarterly periods by which the corporation has the right to defer interest payments on junior subordinated deferrable interest debentures | quarter |  | 20 |  |
Cullen Frost Capital Trust II [Member] |  |  |  |
Borrowed Funds [Line Items] |  |  |  |
Maturity date |  |  |  | Mar. 01, 2034
Proceeds from Issuance of Trust Preferred Securities |  |  |  | $ 120,000
Floating rate 3 month SOFR plus margin |  |  |  | 1.81%
Proceeds from issuance of Common Equity Securities |  |  |  | $ 3,700
Federal Funds Purchased [Member] | Minimum [Member] |  |  |  |
Borrowed Funds [Line Items] |  |  |  |
Short term debt maturity period |  | 1 day |  |
Federal Funds Purchased [Member] | Maximum [Member] |  |  |  |
Borrowed Funds [Line Items] |  |  |  |
Short term debt maturity period |  | 90 days |  |
Securities Loaned or Sold under Agreements to Repurchase [Member] | Minimum [Member] |  |  |  |
Borrowed Funds [Line Items] |  |  |  |
Short term debt maturity period |  | 30 days |  |
Securities Loaned or Sold under Agreements to Repurchase [Member] | Maximum [Member] |  |  |  |
Borrowed Funds [Line Items] |  |  |  |
Short term debt maturity period |  | 90 days |  |
Subordinated Debt [Member] |  |  |  |
Borrowed Funds [Line Items] |  |  |  |
Subordinated notes | $ 100,000 |  |  |
Subordinated notes interest rate | 4.50% |  |  |
Maturity date | Mar. 17, 2027 |  |  |
Unamortized debt issuance cost related to note |  | $ 352 | 509 |
Junior Subordinated Deferrable Interest Debenture [Member] | Cullen Frost Capital Trust II [Member] |  |  |  |
Borrowed Funds [Line Items] |  |  |  |
Unamortized debt issuance cost related to note |  | 528 | 585 |
Junior subordinated deferrable interest debentures |  | $ 123,700 | $ 123,700 | $ 123,700
Floating rate 3 month SOFR plus margin |  | 6.28% | 7.19% |

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- Definition Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(13)(1)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.12-12A(Column A)(Footnote 2)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477271/946-320-S99-2 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-12(Column A)(Footnote 2)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477271/946-320-S99-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 6 -Subparagraph (SX 210.12-14(Column A)(Footnote 2)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477271/946-320-S99-6 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-12B(Column A)(Footnote 4)(b)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477271/946-320-S99-3 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483466/210-20-50-3 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(m)(1)(i)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(m)(1)(ii)(A)(i)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 10 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483444/210-20-55-10 + Details
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