Notes Payable - Additional Information (Detail) - USD ($)	3 Months Ended
Mar. 31, 2021	May 23, 2019
Debt Instrument [Line Items]
Interest only, payment term	36 months
Bio Pharma Credit Plc
Debt Instrument [Line Items]
Secured credit term loan		$ 60,000,000.0
Additional facility funds that can be obtained		$ 20,000,000
Bio Pharma Credit Plc \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, term	72 months
Basis spread on variable rate	7.50%
LIBOR floor rate	2.00%

Additional Amount Of Debt Facility that Can be availed

No definition available.

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Namespace Prefix:	bdsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Debt Instrument, Interest Only Payment Term

+ References

No definition available.

+ Details

Name:	bdsi_DebtInstrumentInterestOnlyPaymentTerm
Namespace Prefix:	bdsi_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Variable Rate, Floor Interest Rate

+ References

No definition available.

+ Details

Name:	bdsi_DebtInstrumentVariableRateFloorInterestRate
Namespace Prefix:	bdsi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=bdsi_BioPharmaCreditPlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: