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Regulatory Capital Requirements (Details) | Dec. 31, 2025 USD ($) shares | Dec. 31, 2024 USD ($) shares
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Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Total capital | $ 446,560,000 | $ 429,208,000
Total capital to risk weighted assets ratio | 0.1277 | 0.1211
Total capital required for capital adequacy | $ 279,756,000 | $ 283,628,000
Total capital required for capital adequacy to risk-weighted assets ratio | 0.0800 | 0.0800
Total capital required for capital adequacy with capital conservation buffer | $ 367,180,000 | $ 372,261,000
Total capital required for capital adequacy with capital conservation buffer to risk-weighted assets ratio | 10.50% | 10.50%
Total capital required to be well-capitalized | $ 349,695,000 | $ 354,535,000
Total capital required to be well-capitalized to risk-weighted assets ratio | 0.1000 | 0.1000
Tier one risk-based capital | $ 354,490,000 | $ 337,232,000
Tier one risk-based capital to risk-weighted assets ratio | 0.1014 | 0.0951
Tier one risk-based capital required for capital adequacy | $ 209,817,000 | $ 212,721,000
Tier one risk-based capital required for capital adequacy to risk-weighted assets ratio | 0.0600 | 0.0600
Tier one risk-based capital required for capital adequacy with capital conservation buffer | $ 297,241,000 | $ 301,354,000
Tier one risk-based capital required for capital adequacy with capital conservation buffer to risk-weighted assets ratio | 8.50% | 8.50%
Tier one risk-based capital required to be well-capitalized | $ 279,756,000 | $ 283,628,000
Tier one risk-based capital required to be well-capitalized to risk-weighted assets ratio | 0.0800 | 0.0800
Common equity tier one risk-based capital | $ 334,490,000 | $ 317,232,000
Common equity tier one risk-based capital to risk-weighted assets ratio | 0.0957 | 0.0895
Common equity tier one risk-based capital required for capital adequacy | $ 157,363,000 | $ 159,541,000
Common equity tier one risk-based capital required for capital adequacy to risk-weighted assets ratio | 0.0450 | 0.0450
Common equity tier one risk-based capital required for capital adequacy with capital conservation buffer | $ 244,786,000 | $ 248,174,000
Common equity tier one risk-based capital required for capital adequacy with capital conservation buffer to risk-weighted assets ratio | 7.00% | 7.00%
Common equity tier one risk-based capital required to be well-capitalized | $ 227,302,000 | $ 230,447,000
Common equity tier one risk-based capital required to be well-capitalized to risk-weighted assets ratio | 0.0650 | 0.0650
Tier one leverage capital | $ 354,490,000 | $ 337,232,000
Tier one leverage capital to average assets ratio | 0.0844 | 0.0793
Tier one leverage capital required for capital adequacy | $ 168,074,000 | $ 170,113,000
Tier one leverage capital required for capital adequacy to average assets ratio | 0.0400 | 0.0400
Tier one leverage capital required for capital adequacy with capital conservation buffer | $ 168,074,000 | $ 170,113,000
Tier one leverage capital required for capital adequacy with capital conservation buffer to average assets ratio | 4.00% | 4.00%
Tier one leverage capital required to be well-capitalized | $ 210,092,000 | $ 212,641,000
Tier one leverage capital required to be well-capitalized to average assets ratio | 0.0500 | 0.0500
Tangible capital to tangible assets ratio | 0.0642 | 0.0568
Intangible assets | $ 0 | $ 0
Preferred stock, shares outstanding | shares | 0 | 0
West Bank [Member] |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Total capital | $ 466,888,000 | $ 455,572,000
Total capital to risk weighted assets ratio | 0.1335 | 0.1286
Total capital required for capital adequacy | $ 279,703,000 | $ 283,468,000
Total capital required for capital adequacy to risk-weighted assets ratio | 0.0800 | 0.0800
Total capital required for capital adequacy with capital conservation buffer | $ 367,110,000 | $ 372,051,000
Total capital required for capital adequacy with capital conservation buffer to risk-weighted assets ratio | 10.50% | 10.50%
Total capital required to be well-capitalized | $ 349,629,000 | $ 354,335,000
Total capital required to be well-capitalized to risk-weighted assets ratio | 0.1000 | 0.1000
Tier one risk-based capital | $ 434,818,000 | $ 423,596,000
Tier one risk-based capital to risk-weighted assets ratio | 0.1244 | 0.1195
Tier one risk-based capital required for capital adequacy | $ 209,777,000 | $ 212,601,000
Tier one risk-based capital required for capital adequacy to risk-weighted assets ratio | 0.0600 | 0.0600
Tier one risk-based capital required for capital adequacy with capital conservation buffer | $ 297,184,000 | $ 301,184,000
Tier one risk-based capital required for capital adequacy with capital conservation buffer to risk-weighted assets ratio | 8.50% | 8.50%
Tier one risk-based capital required to be well-capitalized | $ 279,703,000 | $ 283,468,000
Tier one risk-based capital required to be well-capitalized to risk-weighted assets ratio | 0.0800 | 0.0800
Common equity tier one risk-based capital | $ 434,818,000 | $ 423,596,000
Common equity tier one risk-based capital to risk-weighted assets ratio | 0.1244 | 0.1195
Common equity tier one risk-based capital required for capital adequacy | $ 157,333,000 | $ 159,451,000
Common equity tier one risk-based capital required for capital adequacy to risk-weighted assets ratio | 0.0450 | 0.0450
Common equity tier one risk-based capital required for capital adequacy with capital conservation buffer | $ 244,740,000 | $ 248,034,000
Common equity tier one risk-based capital required for capital adequacy with capital conservation buffer to risk-weighted assets ratio | 7.00% | 7.00%
Common equity tier one risk-based capital required to be well-capitalized | $ 227,259,000 | $ 230,317,000
Common equity tier one risk-based capital required to be well-capitalized to risk-weighted assets ratio | 0.0650 | 0.0650
Tier one leverage capital | $ 434,818,000 | $ 423,596,000
Tier one leverage capital to average assets ratio | 0.1035 | 0.0997
Tier one leverage capital required for capital adequacy | $ 168,053,000 | $ 170,029,000
Tier one leverage capital required for capital adequacy to average assets ratio | 0.0400 | 0.0400
Tier one leverage capital required for capital adequacy with capital conservation buffer | $ 168,053,000 | $ 170,029,000
Tier one leverage capital required for capital adequacy with capital conservation buffer to average assets ratio | 4.00% | 4.00%
Tier one leverage capital required to be well-capitalized | $ 210,067,000 | $ 212,537,000
Tier one leverage capital required to be well-capitalized to average assets ratio | 0.0500 | 0.0500

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- Definition The minimum common equity tier one risk-based capital ratio including the capital conservation buffer. + References No definition available. + Details
Name: | wtba_CommonEquityTierOneRiskBasedCapitalRatioCapitalAdequacyWithCapitalConservationBufferToRiskWeightedAssetsMinimum
Namespace Prefix: | wtba_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The minimum amount of tier one leverage capital required for capital adequacy purposes plus the capital conservation buffer. + References No definition available. + Details
Name: | wtba_TierOneLeverageCapitalCapitalAdequacyWithCapitalConservationBufferMinimum
Namespace Prefix: | wtba_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The minimum amount of tier one leverage capital for capital adequacy purposes plus the capital conservation buffer divided by average assets as defined in the regulations. + References No definition available. + Details
Name: | wtba_TierOneLeverageCapitalRatioCapitalAdequacyWithCapitalConservationBufferToAverageAssetsMinimum
Namespace Prefix: | wtba_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition The minimum amount of tier one risk-based capital required for capital adequacy purposes plus the capital conservation buffer. + References No definition available. + Details
Name: | wtba_TierOneRiskBasedCapitalCapitalAdequacyWithCapitalConservationBufferMinimum
Namespace Prefix: | wtba_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The minimum Tier One Risk Based Capital ratio including the capital conservation buffer. + References No definition available. + Details
Name: | wtba_TierOneRiskBasedCapitalRatioCapitalAdequacyWithCapitalConservationBufferMinimumToRiskWeightedAssets
Namespace Prefix: | wtba_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The minimum amount of total risk-based capital required for capital adequacy purposes plus the capital conservation buffer. + References No definition available. + Details
Name: | wtba_TotalRiskBasedCapitalCapitalAdequacyWithCapitalConservationBufferMinimum
Namespace Prefix: | wtba_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The minimum total risk-based capital based ratio including the capital conservation buffer. + References No definition available. + Details
Name: | wtba_TotalRiskBasedCapitalRatioCapitalAdequacyWithCapitalConservationBufferToRiskWeightedAssetsMinimum
Namespace Prefix: | wtba_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | dei_LegalEntityAxis=wtba_WestBankMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |