Financial Highlights (Tables)

12 Months Ended

Sep. 30, 2025

Investment Company [Abstract]

Schedule of Investment Company, Financial Highlights

The financial highlights for the Company are as follows:

	Year ended September 30,
Per share data:(1)	2025				2024				2023			2022				2021
Net asset value at beginning of period	$	15.19			$	15.02			$	14.89		$	15.19			$	14.33
Net increase in net assets as a result of issuance of DRIP shares	0.00			(2)	0.00			(2)	—			0.00			(2)	0.00			(2)
Net increase (decrease) in net assets as a result of issuance of shares	0.00			(2)	0.51			(3)	—			—				—
Net increase in net assets as a result of repurchases of shares	0.01				0.00			(2)	0.01			—				—
Distributions declared:
From net investment income - after tax	(1.36)				(1.89)				(1.23)			(1.20)				(1.13)
From capital gains	—				—				(0.17)			—				(0.03)
From return of capital	(0.29)				—				—			—				—
Net investment income - after tax	1.49				1.90				1.70			1.15				0.99
Net realized gain (loss) on investment transactions	(0.27)				(0.40)				(0.26)			0.12				0.05
Net realized gain (loss) on extinguishment of debt	(0.00)			(2)	—				—			—				—
Net change in unrealized appreciation (depreciation) on investment transactions(4)	0.20				0.05				0.08			(0.37)				0.98
Net asset value at end of period	$	14.97			$	15.19			$	15.02		$	14.89			$	15.19
Per share market value at end of period	$	13.69			$	15.11			$	14.67		$	12.39			$	15.81
Total return based on market value(5)	0.79		%		15.77		%		30.50		%	(14.80)		%		28.90		%
Number of common shares outstanding	266,008,083				264,277,128				169,594,742			170,895,670				170,028,584

	Year ended September 30,
Listed below are supplemental data and ratios to the financial highlights:	2025	2024	2023	2022	2021
Ratio of net investment income - after tax to average net assets	9.87%	12.55%	11.46%	7.53%	6.73%
Ratio of total expenses to average net assets	11.77%	12.12%	12.45%	7.43%	5.78%
Ratio of management fee waiver to average net assets	—%	—%	—%	(0.07)%	(0.16)%
Ratio of incentive fee waiver to average net assets	—%	(0.90)%	—%	—%	—%
Ratio of incentive fees to average net assets	1.82%	2.53%	2.94%	0.68%	0.13%
Ratio of income and excise taxes to average net assets	(0.01)%	0.04%	0.15%	—%	—%
Ratio of net expenses (without incentive fees) to average net assets	9.95%	9.59%	9.51%	6.68%	5.49%
Total return based on average net asset value(6)	9.36%	8.98%	10.25%	5.89%	13.70%
Net assets at end of period	$3,982,567	$4,014,529	$2,547,878	$2,544,500	$2,582,692
Average debt outstanding	$4,892,712	$3,492,575	$3,069,412	$2,935,846	$2,184,010
Average debt outstanding per share	$18.39	$13.22	$18.10	$17.18	$12.84
Portfolio turnover	17.55%	20.29%	12.19%	23.56%	35.58%
Asset coverage ratio(7)	180.21%	185.96%	180.68%	181.70%	200.04%

(1)Based on actual number of shares outstanding at the end of the corresponding period or the weighted average shares outstanding for the period, unless otherwise noted, as appropriate.

(2)Represents an amount less than $0.01.

(3)Net increase in net assets as a result of issuance of shares pursuant to the GBDC 3 Merger.

(4)Includes the impact of different share amounts as a result of calculating certain per share data based on weighted average shares outstanding during the period and certain per share data based on the shares outstanding at the end of the period and as of the dividend record date.

(5)Total return based on market value assumes distributions are reinvested in accordance with the DRIP. Total return does not include sales load.

(6)Total return based on average net asset value is calculated as (a) the net increase (decrease) in net assets resulting from operations divided by (b) the daily average of total net assets. Total return does not include sales load.

(7)Effective February 6, 2019, in accordance with Section 61(a)(2) of the 1940 Act, with certain limited exceptions, the Company is allowed to borrow amounts such that its asset coverage, as defined in the 1940 Act, is at least 150% after such borrowing (excluding the Company's SBA debentures pursuant to exemptive relief received by the Company from the SEC). Prior to February 6, 2019, in accordance with the 1940 Act, with certain limited exceptions, the Company was allowed to borrow amounts such that its asset coverage, as defined in the 1940 Act, was at least 200% after such borrowing (excluding the Company's SBA debentures pursuant to exemptive relief received by the Company from the SEC).