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Note 22 - Regulatory Matters (Details) - Capital and Leverage Ratios (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Company [Member] |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Tier I Capital (to risk- weighted assets) | $ 1,406,511 us-gaap_TierOneRiskBasedCapital / dei_LegalEntityAxis = caty_CompanyMember |  | $ 1,288,892 us-gaap_TierOneRiskBasedCapital / dei_LegalEntityAxis = caty_CompanyMember |
Tier I Capital (to risk- weighted assets) | 14.96%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_CompanyMember |  | 15.04%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_CompanyMember |
Tier I Capital minimum requirement | 376,072 us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized / dei_LegalEntityAxis = caty_CompanyMember |  | 342,899 us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized / dei_LegalEntityAxis = caty_CompanyMember |
Tier I Capital minimum requirement | 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = caty_CompanyMember |  | 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = caty_CompanyMember |
Excess | 1,030,439 us-gaap_ExcessTierOneRiskBasedCapital / dei_LegalEntityAxis = caty_CompanyMember |  | 945,993 us-gaap_ExcessTierOneRiskBasedCapital / dei_LegalEntityAxis = caty_CompanyMember |
Excess | 10.96%us-gaap_ExcessTierOneRiskBasedCapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_CompanyMember |  | 11.04%us-gaap_ExcessTierOneRiskBasedCapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_CompanyMember |
Total Capital (to risk- weighted assets) | 1,524,702 us-gaap_Capital / dei_LegalEntityAxis = caty_CompanyMember |  | 1,401,319 us-gaap_Capital / dei_LegalEntityAxis = caty_CompanyMember |
Total Capital (to risk- weighted assets) | 16.22%us-gaap_CapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_CompanyMember |  | 16.35%us-gaap_CapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_CompanyMember |
Total Capital minimum requirement | 752,144 us-gaap_CapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = caty_CompanyMember |  | 685,799 us-gaap_CapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = caty_CompanyMember |
Total Capital minimum requirement | 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = caty_CompanyMember |  | 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = caty_CompanyMember |
Excess | 772,558 us-gaap_ExcessCapital / dei_LegalEntityAxis = caty_CompanyMember |  | 715,520 us-gaap_ExcessCapital / dei_LegalEntityAxis = caty_CompanyMember |
Excess | 8.22%us-gaap_ExcessCapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_CompanyMember |  | 8.35%us-gaap_ExcessCapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_CompanyMember |
Tier I Capital (to average assets) Leverage ratio | 1,406,511 us-gaap_TierOneLeverageCapital / dei_LegalEntityAxis = caty_CompanyMember |  | 1,288,892 us-gaap_TierOneLeverageCapital / dei_LegalEntityAxis = caty_CompanyMember |
Tier I Capital (to average assets) Leverage ratio | 12.99%us-gaap_TierOneLeverageCapitalToAverageAssets / dei_LegalEntityAxis = caty_CompanyMember |  | 12.48%us-gaap_TierOneLeverageCapitalToAverageAssets / dei_LegalEntityAxis = caty_CompanyMember |
Minimum leverage requirement | 433,121 us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = caty_CompanyMember |  | 413,158 us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = caty_CompanyMember |
Minimum leverage requirement | 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets / dei_LegalEntityAxis = caty_CompanyMember |  | 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets / dei_LegalEntityAxis = caty_CompanyMember |
Excess | 973,390 us-gaap_ExcessTierOneLeverageCapital / dei_LegalEntityAxis = caty_CompanyMember |  | 875,734 us-gaap_ExcessTierOneLeverageCapital / dei_LegalEntityAxis = caty_CompanyMember |
Excess | 8.99%us-gaap_ExcessTierOneLeverageCapitalToAverageAssets / dei_LegalEntityAxis = caty_CompanyMember |  | 8.48%us-gaap_ExcessTierOneLeverageCapitalToAverageAssets / dei_LegalEntityAxis = caty_CompanyMember |
Total average assets (1) | 10,828,015 caty_AverageAssetsTotal / dei_LegalEntityAxis = caty_CompanyMember | [1] | 10,328,952 caty_AverageAssetsTotal / dei_LegalEntityAxis = caty_CompanyMember | [1]
Risk-weighted assets | 9,401,803 us-gaap_RiskWeightedAssets / dei_LegalEntityAxis = caty_CompanyMember |  | 8,572,487 us-gaap_RiskWeightedAssets / dei_LegalEntityAxis = caty_CompanyMember |
Bank [Member] |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Tier I Capital (to risk- weighted assets) | 1,353,481 us-gaap_TierOneRiskBasedCapital / dei_LegalEntityAxis = caty_BankMember |  | 1,244,480 us-gaap_TierOneRiskBasedCapital / dei_LegalEntityAxis = caty_BankMember |
Tier I Capital (to risk- weighted assets) | 14.42%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_BankMember |  | 14.53%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_BankMember |
Tier I Capital minimum requirement | 375,318 us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized / dei_LegalEntityAxis = caty_BankMember |  | 342,701 us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized / dei_LegalEntityAxis = caty_BankMember |
Tier I Capital minimum requirement | 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = caty_BankMember |  | 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = caty_BankMember |
Excess | 978,163 us-gaap_ExcessTierOneRiskBasedCapital / dei_LegalEntityAxis = caty_BankMember |  | 901,779 us-gaap_ExcessTierOneRiskBasedCapital / dei_LegalEntityAxis = caty_BankMember |
Excess | 10.42%us-gaap_ExcessTierOneRiskBasedCapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_BankMember |  | 10.53%us-gaap_ExcessTierOneRiskBasedCapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_BankMember |
Total Capital (to risk- weighted assets) | 1,471,337 us-gaap_Capital / dei_LegalEntityAxis = caty_BankMember |  | 1,352,415 us-gaap_Capital / dei_LegalEntityAxis = caty_BankMember |
Total Capital (to risk- weighted assets) | 15.68%us-gaap_CapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_BankMember |  | 15.79%us-gaap_CapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_BankMember |
Total Capital minimum requirement | 750,637 us-gaap_CapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = caty_BankMember |  | 685,402 us-gaap_CapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = caty_BankMember |
Total Capital minimum requirement | 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = caty_BankMember |  | 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = caty_BankMember |
Excess | 720,700 us-gaap_ExcessCapital / dei_LegalEntityAxis = caty_BankMember |  | 667,013 us-gaap_ExcessCapital / dei_LegalEntityAxis = caty_BankMember |
Excess | 7.68%us-gaap_ExcessCapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_BankMember |  | 7.79%us-gaap_ExcessCapitalToRiskWeightedAssets / dei_LegalEntityAxis = caty_BankMember |
Tier I Capital (to average assets) Leverage ratio | 1,353,481 us-gaap_TierOneLeverageCapital / dei_LegalEntityAxis = caty_BankMember |  | 1,244,480 us-gaap_TierOneLeverageCapital / dei_LegalEntityAxis = caty_BankMember |
Tier I Capital (to average assets) Leverage ratio | 12.52%us-gaap_TierOneLeverageCapitalToAverageAssets / dei_LegalEntityAxis = caty_BankMember |  | 12.06%us-gaap_TierOneLeverageCapitalToAverageAssets / dei_LegalEntityAxis = caty_BankMember |
Minimum leverage requirement | 432,350 us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = caty_BankMember |  | 412,815 us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = caty_BankMember |
Minimum leverage requirement | 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets / dei_LegalEntityAxis = caty_BankMember |  | 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets / dei_LegalEntityAxis = caty_BankMember |
Excess | 921,131 us-gaap_ExcessTierOneLeverageCapital / dei_LegalEntityAxis = caty_BankMember |  | 831,665 us-gaap_ExcessTierOneLeverageCapital / dei_LegalEntityAxis = caty_BankMember |
Excess | 8.52%us-gaap_ExcessTierOneLeverageCapitalToAverageAssets / dei_LegalEntityAxis = caty_BankMember |  | 8.06%us-gaap_ExcessTierOneLeverageCapitalToAverageAssets / dei_LegalEntityAxis = caty_BankMember |
Total average assets (1) | 10,808,747 caty_AverageAssetsTotal / dei_LegalEntityAxis = caty_BankMember | [1] | 10,320,368 caty_AverageAssetsTotal / dei_LegalEntityAxis = caty_BankMember | [1]
Risk-weighted assets | $ 9,382,961 us-gaap_RiskWeightedAssets / dei_LegalEntityAxis = caty_BankMember |  | $ 8,567,523 us-gaap_RiskWeightedAssets / dei_LegalEntityAxis = caty_BankMember |
[1] | Average assets represent average balances for the fourth quarter of each year presented.

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- Definition The amount of total capital as defined in the regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 948 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47304-110998 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 948 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47080-110998 + Details
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- Definition The minimum amount of Total Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826 + Details
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- Definition Total Capital divided by risk weighted assets as defined in the regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The amount by which the company's Total Capital exceeds the minimum required for capital adequacy purposes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The amount of excess Total Capital divided by risk weighted assets which are assets that are weighted for credit risk according to a formula used by the Reserve Bank. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826 + Details
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- Definition The amount by which the company's Tier 1 Leverage Capital exceeds the minimum required for capital adequacy purposes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The amount of excess Tier 1 Leverage Capital divided by average assets as defined in the regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The amount by which the company's Tier 1 Risk Based Capital exceeds the minimum required for capital adequacy purposes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The amount of excess Tier 1 Risk Based Capital (which consists of the types of financial capital considered the most reliable and liquid, primarily Shareholders' equity. Examples of Tier 1 capital are common stock or unit, preferred stock or unit that is irredeemable and noncumulative, and retained earnings) divided by risk-weighted assets which are assets that are weighted for credit risk according to a formula used by the Reserve Bank. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The minimum amount of Tier 1 Leverage Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826 + Details
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- Definition Tier 1 Risk Based Capital as defined in the regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826 + Details
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- Definition The amount of Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition Tier 1 capital divided by risk weighted assets as defined by regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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