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Cash Equivalents and Marketable Securities - Additional Information (Details) | 9 Months Ended
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Sep. 30, 2021 USD ($)
Cash And Cash Equivalents [Abstract] |
Realized gains or losses on available-for-sale securities | $ 0
Available-for-sale securities, continuous unrealized loss position, more than 12 months | $ 0
Short-term marketable securities contractual maturities | 7 months

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- Definition Short term marketable securities contractual maturities. + References No definition available. + Details
Name: | bbio_ShortTermMarketableSecuritiesContractualMaturities
Namespace Prefix: | bbio_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer. + References No definition available. + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities. + References No definition available. + Details
Name: | us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_CashAndCashEquivalentsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration