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BORROWINGS - Narrative (Details) € in Millions, £ in Millions, kr in Millions |  | 1 Months Ended | 6 Months Ended | 12 Months Ended |  |  |  |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Nov. 23, 2021 USD ($) | Feb. 28, 2019 USD ($) | Jun. 30, 2023 USD ($) | Dec. 31, 2022 USD ($) | Jun. 30, 2023 SEK (kr) | Jun. 30, 2023 GBP (£) | Jun. 30, 2023 EUR (€) | Dec. 31, 2022 SEK (kr) | Dec. 31, 2022 GBP (£) | Dec. 31, 2022 EUR (€) | Apr. 30, 2022 USD ($) | Apr. 01, 2022 USD ($) | Feb. 25, 2022 USD ($) | Nov. 04, 2021 USD ($) | Feb. 25, 2021 USD ($) | Nov. 04, 2020 USD ($) | Sep. 29, 2020 USD ($) | Sep. 24, 2020 USD ($) | Aug. 03, 2020 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowings under credit facilities |  |  | $ 772,087,000 | $ 729,144,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commitment aggregate amount |  | $ 800,000,000 | $ 1,100,000,000 | 1,100,000,000 |  |  |  |  |  |  |  | $ 1,100,000,000 | $ 965,000,000 | $ 875,000,000 |  |  |  |  |
Line of credit facility commitment aggregate value |  | $ 1,200,000,000 |  |  |  |  |  |  |  |  |  | $ 1,500,000,000 | $ 1,500,000,000 |  |  |  |  |  |
Line of credit, repayment period after maturity |  |  | 1 year |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable floor rate (as percent) |  | 1.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of unused portion of credit facility, greater than two-third of commitments (as percent) |  | 0.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of unused portion of credit facility, less than two-third of commitments (as percent) |  | 0.375% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt issuance costs, financing fees |  | $ 6,400,000 |  |  |  |  |  |  |  |  | $ 4,100,000 |  |  |  |  |  |  |  |
Effective interest rate |  |  | 6.771% |  | 6.771% | 6.771% | 6.771% |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | Line of Credit | Interest Period Of One Month |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, credit spread adjustment |  | 0.0010 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | Line of Credit | Interest Period Of Three Month |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, credit spread adjustment |  | 0.0015 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | Line of Credit | Interest Period Of Six Month |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, credit spread adjustment |  | 0.0025 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | Fair Value, Inputs, Level 3 | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value of long-term debt |  |  | $ 772,100,000 | 729,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | Base Rate | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 1.25% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | Base Rate | Line of Credit | External Credit Rating, Investment Grade |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 1.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | SOFR | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 2.25% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | SOFR | Line of Credit | External Credit Rating, Investment Grade |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 2.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | Applicable Rate | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 2.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | Applicable Rate | Line of Credit | External Credit Rating, Non Investment Grade |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 2.25% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | Screen Rate | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 2.20% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | Screen Rate | Line of Credit | External Credit Rating, Non Investment Grade |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 2.45% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | Federal Funds Purchased | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 0.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | Overnight Bank Funding Rate | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 0.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February 2019 Credit Facility | One-Month Secured Overnight Financing Rate (SOFR) | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 1.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, credit spread adjustment |  | 0.0010 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Denominated In U.S Dollars | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowings under credit facilities |  |  | $ 532,500,000 | $ 497,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Effective interest rate |  |  | 7.238% | 6.324% | 7.238% | 7.238% | 7.238% | 6.324% | 6.324% | 6.324% |  |  |  |  |  |  |  |  |
Debt Denominated In U.S Dollars | One-Month Secured Overnight Financing Rate (SOFR) | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  |  | 5.138% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Denominated In U.S Dollars | LIBOR | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  |  |  | 4.224% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Denominated In Swedish Kronas | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowings under credit facilities |  |  | $ 1,200,000 | $ 1,200,000 | kr 12.8 |  |  | kr 12.8 |  |  |  |  |  |  |  |  |  |  |
Effective interest rate |  |  | 5.563% | 4.375% | 5.563% | 5.563% | 5.563% | 4.375% | 4.375% | 4.375% |  |  |  |  |  |  |  |  |
Debt Denominated In Swedish Kronas | Stockholm Interbank Offered Rate (STIBOR) | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  |  | 3.563% | 2.375% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Denominated In British Pounds | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowings under credit facilities |  |  | $ 87,200,000 | $ 82,500,000 |  | £ 68.6 |  |  | £ 68.6 |  |  |  |  |  |  |  |  |  |
Effective interest rate |  |  | 6.461% | 4.96% | 6.461% | 6.461% | 6.461% | 4.96% | 4.96% | 4.96% |  |  |  |  |  |  |  |  |
Debt Denominated In British Pounds | Sterling Overnight Index Average (SONIA) | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  |  | 4.461% | 2.96% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Denominated In Euro | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowings under credit facilities |  |  | $ 151,200,000 | $ 147,900,000 |  |  | € 138.6 |  |  | € 138.6 |  |  |  |  |  |  |  |  |
Effective interest rate |  |  | 5.313% | 3.625% | 5.313% | 5.313% | 5.313% | 3.625% | 3.625% | 3.625% |  |  |  |  |  |  |  |  |
Debt Denominated In Euro | Euro Interbank Offered Rate (EURIBOR) | Line of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  |  | 3.313% | 1.625% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
August 2025 Notes | Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, ownership percentage for immediate conversion |  |  | 66.67% |  | 66.67% | 66.67% | 66.67% |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 25,000,000 | $ 25,000,000 | $ 50,000,000
Fixed interest rate |  |  | 4.66% |  | 4.66% | 4.66% | 4.66% |  |  |  |  |  |  |  |  |  |  |  | 4.66%
August 2025 Notes | Fair Value, Inputs, Level 3 | Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value of long-term debt |  |  | $ 46,300,000 | $ 46,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
November Notes, Series B Notes | Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 62,500,000 |  |  |
Fixed interest rate |  |  | 4.25% |  | 4.25% | 4.25% | 4.25% |  |  |  |  |  |  |  |  | 4.25% |  |  |
November Notes, Series B Notes | Fair Value, Inputs, Level 3 | Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value of long-term debt |  |  | $ 57,300,000 | 56,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
November Notes, Series C Notes | Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 112,500,000 |  |  |
Fixed interest rate |  |  | 4.75% |  | 4.75% | 4.75% | 4.75% |  |  |  |  |  |  |  |  | 4.75% |  |  |
November Notes, Series C Notes | Fair Value, Inputs, Level 3 | Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value of long-term debt |  |  | $ 98,700,000 | 97,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Series B And Series C Senior Unsecured Notes Due November | Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate extended |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.0075 |  |  |
Investment grade conditions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.0150 |  |  |
February Notes, Series D Notes | Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 80,000,000 |  |  |  |
Fixed interest rate |  |  | 3.41% |  | 3.41% | 3.41% | 3.41% |  |  |  |  |  |  |  | 3.41% |  |  |  |
February Notes, Series D Notes | Fair Value, Inputs, Level 3 | Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value of long-term debt |  |  | $ 70,400,000 | 69,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
February Notes, Series E Notes | Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 70,000,000 |  |  |  |
Fixed interest rate |  |  | 4.06% |  | 4.06% | 4.06% | 4.06% |  |  |  |  |  |  |  | 4.06% |  |  |  |
February Notes, Series E Notes | Fair Value, Inputs, Level 3 | Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value of long-term debt |  |  | $ 58,700,000 | 57,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Series D And Series E Senior Unsecured Notes Due February | Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, ownership percentage for immediate conversion |  |  | 66.67% |  | 66.67% | 66.67% | 66.67% |  |  |  |  |  |  |  |  |  |  |  |
Interest rate extended |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.0075 |  |  |  |
Investment grade conditions |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.0150 |  |  |  |
November 2026 Notes | Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, ownership percentage for immediate conversion |  |  | 66.67% |  | 66.67% | 66.67% | 66.67% |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount | $ 350,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed interest rate | 3.30% |  | 3.30% |  | 3.30% | 3.30% | 3.30% |  |  |  |  |  |  |  |  |  |  |  |
Redemption percentage on purchase price (as percent) | 100.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
November 2026 Notes | Fair Value, Inputs, Level 3 | Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value of long-term debt |  |  | $ 300,300,000 | $ 294,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

X
- Definition Debt Instrument, Credit Spread Adjustment + References No definition available. + Details
Name: | bbdc_DebtInstrumentCreditSpreadAdjustment
Namespace Prefix: | bbdc_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

X
- Definition Debt Instrument, Ownership Percentage For Immediate Conversion + References No definition available. + Details
Name: | bbdc_DebtInstrumentOwnershipPercentageForImmediateConversion
Namespace Prefix: | bbdc_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Debt Instrument, Variable Interest Rate, Floor + References No definition available. + Details
Name: | bbdc_DebtInstrumentVariableInterestRateFloor
Namespace Prefix: | bbdc_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line of credit facility, accordion feature, increase limit, subject to certain conditions by obtaining additional commitments from existing and/or new lenders. + References No definition available. + Details
Name: | bbdc_LineOfCreditFacilityAccordionFeatureAggregateLimit
Namespace Prefix: | bbdc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Line Of Credit Facility, Unused Capacity, Less Than Two-Thirds Of Commitment Fee Percentage + References No definition available. + Details
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