Debt Instrument, Amortization Period

No definition available.

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Namespace Prefix:	gbdc_
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Balance Type:	na
Period Type:	duration

- Definition

Line of Credit Facility, Accordion Feature, Higher Borrowing Capacity Option

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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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.

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+ Details

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- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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- 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.

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- Definition

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

+ References

+ Details

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Borrowings - JPM Credit Facility - Narrative (Details) - USD ($)			9 Months Ended
	Apr. 04, 2025	Apr. 03, 2025	Jun. 30, 2026	Sep. 30, 2025	Dec. 05, 2024
Debt Instrument [Line Items]
Long-term debt			$ 4,537,552,000	$ 4,900,773,000
JPM Credit Facility \| Revolving Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			$ 1,997,500,000		$ 1,822,500,000
Line of credit facility, commitment fee percentage	0.325%	0.375%	0.325%
Line of credit facility, maximum borrowing capacity	$ 3,000,000,000
Debt instrument, amortization period			1 year
Long-term debt			$ 271,559,000	1,098,437,000
JPM Credit Facility \| Revolving Credit Facility \| Line of Credit \| Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.10%
JPM Credit Facility \| Revolving Credit Facility \| Line of Credit \| SONIA
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.0326%
JPM Credit Facility \| Revolving Credit Facility \| Line of Credit \| Canadian Overnight Repo Rate Average
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.02955%
JPM Credit Facility \| Revolving Credit Facility \| Line of Credit \| Bank Bill Swap Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.20%
JPM Credit Facility \| Letter of Credit \| Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			$ 23,750,000
Long-term debt			$ 0	$ 0
JPM Credit Facility - Term Benchmark Loan \| Revolving Credit Facility \| Line of Credit \| Base Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			1.65%
JPM Credit Facility - Term Benchmark Loan \| Revolving Credit Facility \| Line of Credit \| Base Rate \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.525%
JPM Credit Facility - Term Benchmark Loan \| Revolving Credit Facility \| Line of Credit \| Base Rate \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.775%
JPM Credit Facility- ABR Loan \| Revolving Credit Facility \| Line of Credit \| Base Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.65%
JPM Credit Facility- ABR Loan \| Revolving Credit Facility \| Line of Credit \| Base Rate \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	0.525%
JPM Credit Facility- ABR Loan \| Revolving Credit Facility \| Line of Credit \| Base Rate \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	0.775%