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Securities - Schedule of Investment Securities with Unrealized Loss (Parenthetical) (Details) - USD ($) $ in Thousands | Jun. 30, 2025 | Dec. 31, 2024
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Investments, Debt and Equity Securities [Abstract] |  |
Fair value amount of allowance for credit loss reserve | $ 3,000 | $ 4,000

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- Definition Fair value amount of allowance for credit losses reserve. + References No definition available. + Details
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Namespace Prefix: | bvfl_
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Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration