Related Party Transactions (Details)		3 Months Ended		9 Months Ended		12 Months Ended				46 Months Ended
Related Party Transactions (Details)	Apr. 01, 2022 USD ($) shares	Jun. 30, 2025 USD ($) component shares	Jun. 30, 2024 USD ($)	Jun. 30, 2025 USD ($) component shares	Jun. 30, 2024 USD ($)	Mar. 31, 2025	Sep. 30, 2024 USD ($) shares	Mar. 31, 2024	Mar. 31, 2023	Jun. 30, 2025 USD ($) component shares	May 21, 2024 USD ($) shares
Related Party Transaction [Line Items]
Investment company, management and service fees, base rate waiver, percentage of base management fee payable (as a percent)				(0.21%)	(0.49%)
Base management fee		$ 885,000	$ 578,000	$ 2,515,000	$ 1,427,000
Base management fee waived		0	193,000	543,000	759,000
Subscriptions		$ 401,191,000		$ 401,191,000			$ 378,341,000			$ 401,191,000
Common stock, shares issued (in shares) \| shares		24,900,243.606		24,900,243.606			20,412,978.874			24,900,243.606
Contributions		$ 373,107,000		$ 373,107,000			$ 305,798,000			$ 373,107,000
Related Party
Related Party Transaction [Line Items]
Incentive fee		783,000	628,000	2,349,000	1,609,000
Capital gain incentive fee payable		435,000		435,000			364,000			435,000
Accrual of capital gain incentive fee		5,000	114,000	71,000	273,000
Related Party \| Revolving Credit Facility
Related Party Transaction [Line Items]
Line of credit facility, maximum borrowing capacity		75,000,000		75,000,000						75,000,000
Related Party \| GGP Class B-P, LLC
Related Party Transaction [Line Items]
Subscriptions		$ 40,011,000		$ 40,011,000						$ 40,011,000
Increase commitment capital											$ 15,000,000
Common stock, shareholders (in shares) \| shares		550,000		550,000						550,000	550,000
Common stock, shares issued (in shares) \| shares		2,480,650.997		2,480,650.997						2,480,650.997
Contributions		$ 37,210,000		$ 37,210,000						$ 37,210,000
Common stock, shares, issued, dividend reinvestment plan (in shares) \| shares		26,412.009		26,412.009						26,412.009
Related Party \| GGP Class B-P, LLC \| Common Stock \| GGP Holdings LP
Related Party Transaction [Line Items]
Related party transaction, share transferred (in shares) \| shares	700.000
Investment Advisory Agreement \| Related Party
Related Party Transaction [Line Items]
Management and service fee, number of components \| component		2		2						2
Management and service fees, base rate (as a percent)				1.00%
Management and service fees, cash equivalents maturity period (in days)				270 days
Investment company, management and service fees, base rate waiver, percentage of base management fee payable (as a percent)						33.30%		66.70%	100.00%
Base management fee		$ 885,000	578,000	$ 2,515,000	1,427,000
Base management fee waived		$ 0	193,000	$ 543,000	759,000
Number of incentive fee components \| component		3		3						3
Capital gain incentive fee payable		$ 0		$ 0			0			$ 0
Management and service fees, incentive rate cap, percentage of cumulative pre-incentive fee net income (as a percent)				10.00%
Investment Advisory Agreement \| Investment, Administrator
Related Party Transaction [Line Items]
Investment company, excess expense reimbursable		137,000	$ 208,000	$ 576,000	$ 548,000
Investment Management Agreement - Incentive Rate, Quarterly Hurdle Rate \| Related Party
Related Party Transaction [Line Items]
Management and service fees, incentive rate (as a percent)				1.00%
Investment Management Agreement - Quarterly Incentive Rate, Criteria Not Met \| Related Party
Related Party Transaction [Line Items]
Management and service fees, incentive rate (as a percent)				0.00%
Investment Management Agreement - Incentive Rate, Pre-Incentive Fee Net Investment Income Below Catch-Up \| Related Party
Related Party Transaction [Line Items]
Management and service fees, incentive rate (as a percent)				100.00%
Investment Advisory Agreement, Cumulative Pre-Incentive Fee Net Investment Income \| Related Party
Related Party Transaction [Line Items]
Management and service fees, incentive rate (as a percent)				10.00%
Investment Advisory Agreement, Capital Gain Incentive Fee Base \| Related Party
Related Party Transaction [Line Items]
Management and service fees, incentive rate (as a percent)				10.00%
Investment Advisory Agreement, Subordinated Liquidation Incentive Fee Base \| Related Party
Related Party Transaction [Line Items]
Management and service fees, incentive rate (as a percent)				10.00%
Administration Agreement \| Related Party
Related Party Transaction [Line Items]
Accounts payable and other liabilities		122,000		$ 122,000			85,000			122,000
Investment, Adviser \| Related Party
Related Party Transaction [Line Items]
Organization costs and professional fees										56,000
Investment company, excess expense reimbursable				700,000
Formation and Initial Closing Cost Paid \| Related Party
Related Party Transaction [Line Items]
Investment company, excess expense reimbursable				301,000			301,000
Expenses Paid \| Investment, Administrator
Related Party Transaction [Line Items]
Accounts payable and other liabilities		$ 157,000		$ 157,000			$ 164,000			$ 157,000
Conversion to Maryland Corporation, Acquisition of Stock \| Related Party \| GGP Holdings LP
Related Party Transaction [Line Items]
Sale of stock, number of shares issued in transaction (in shares) \| shares	700.000
Subscriptions	$ 11,000
Subscription Agreement \| Related Party \| GGP Class B-P, LLC. GGP Class B-P, LLC
Related Party Transaction [Line Items]
Subscriptions	$ 25,000,000

Golub Capital Direct Lending Unlevered Corp 10-Q