Commitments and Contingencies - Schedule of Unfunded Commitments by Investment (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	$ 286,047	$ 311,361
Investment, Identifier [Axis]: 107 Fair Street LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	3,507
Investment, Identifier [Axis]: 107-109 Beech OAK22 LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	13,567	11,911
Investment, Identifier [Axis]: 112-126 Van Houten Real22 LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	1,077
Investment, Identifier [Axis]: ACESO Holding 4 S.A.R.L.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	4,700
Investment, Identifier [Axis]: ASP Integrity Acquisition Co LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	5,042	0
Investment, Identifier [Axis]: ASP-R-PAC Acquisition Co LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	287	166
Investment, Identifier [Axis]: AVSC Holding Corp.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	5,539	0
Investment, Identifier [Axis]: Accession Risk Management Group, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	11,019
Investment, Identifier [Axis]: Accupac, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	4,051
Investment, Identifier [Axis]: Acquia Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	1,625
Investment, Identifier [Axis]: All Web Leads, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	360	240
Investment, Identifier [Axis]: Amspec Parent LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	9,372
Investment, Identifier [Axis]: Avalara, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	5,047
Investment, Identifier [Axis]: Bayou Intermediate II, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	5,509	0
Investment, Identifier [Axis]: Berner Food & Beverage, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,998	1,007
Investment, Identifier [Axis]: BioXcel Therapeutics, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	7,506	9,383
Investment, Identifier [Axis]: CIELO BIDCO LIMITED
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,555	0
Investment, Identifier [Axis]: Centralsquare Technologies, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,404	1,436
Investment, Identifier [Axis]: Coupa Holdings, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	2,075	2,075
Investment, Identifier [Axis]: Creek Parent, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	6,855	0
Investment, Identifier [Axis]: Crewline Buyer, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	2,180	2,180
Investment, Identifier [Axis]: Delta Leasing SPV II LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	3,581
Investment, Identifier [Axis]: Dialyze Holdings, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,232	0
Investment, Identifier [Axis]: Digital.AI Software Holdings, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	5,238	6,045
Investment, Identifier [Axis]: Dominion Diagnostics, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	5,574
Investment, Identifier [Axis]: Draken International, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	5,873	0
Investment, Identifier [Axis]: EMPIRE BIDCO AB
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	10,609	0
Investment, Identifier [Axis]: Enverus Holdings, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	2,140	3,014
Investment, Identifier [Axis]: Establishment Labs Holdings Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	3,384
Investment, Identifier [Axis]: Everbridge, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	5,043	5,043
Investment, Identifier [Axis]: Evergreen IX Borrower 2023, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,626	1,626
Investment, Identifier [Axis]: Eyesouth Eye Care Holdco LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	2,817	6,585
Investment, Identifier [Axis]: F&M Buyer LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	3,212	0
Investment, Identifier [Axis]: Finastra USA, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	654
Investment, Identifier [Axis]: Galileo Parent, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,596	1,163
Investment, Identifier [Axis]: Grand River Aseptic Manufacturing, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	2,594	0
Investment, Identifier [Axis]: Grove Hotel Parcel Owner, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,762	1,762
Investment, Identifier [Axis]: Harrow, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	3,438
Investment, Identifier [Axis]: Icefall Parent, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,765	995
Investment, Identifier [Axis]: Integrity Marketing Acquisition, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	8,870	16,436
Investment, Identifier [Axis]: Inventus Power, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	2,907	3,792
Investment, Identifier [Axis]: Kings Buyer, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	5,821	3,277
Investment, Identifier [Axis]: Kite Midco II Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	2,374	0
Investment, Identifier [Axis]: LDS Buyer, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,908	0
Investment, Identifier [Axis]: LSL Holdco, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	848	636
Investment, Identifier [Axis]: Legends Hospitality Holding Company, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	2,909	4,651
Investment, Identifier [Axis]: Lightbox Intermediate, L.P.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,268	0
Investment, Identifier [Axis]: MHE Intermediate Holdings, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,071	1,786
Investment, Identifier [Axis]: MRI Software LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	4,092	6,972
Investment, Identifier [Axis]: Mindbody, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	4,027	5,238
Investment, Identifier [Axis]: Minotaur Acquisition, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,882	1,882
Investment, Identifier [Axis]: Monotype Imaging Holdings Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	7,176	8,005
Investment, Identifier [Axis]: Nellson Nutraceutical, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	2,241	0
Investment, Identifier [Axis]: Next Holdco, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	7,051	7,051
Investment, Identifier [Axis]: OCSI Glick JV LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	13,998	13,998
Investment, Identifier [Axis]: Optimizely North America Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,694	0
Investment, Identifier [Axis]: Oranje Holdco, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	1,904
Investment, Identifier [Axis]: PAI Financing Merger Sub LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	5,210	0
Investment, Identifier [Axis]: PPW Aero Buyer, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	13,574	10,235
Investment, Identifier [Axis]: PRGX Global, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	3,127
Investment, Identifier [Axis]: PetVet Care Centers, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	13,732	13,732
Investment, Identifier [Axis]: Pluralsight, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	8,688	8,688
Investment, Identifier [Axis]: Poseidon Midco AB
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	8,144	8,181
Investment, Identifier [Axis]: Protein For Pets Opco, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,545	2,117
Investment, Identifier [Axis]: Quantum Bidco Limited
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	6,311
Investment, Identifier [Axis]: SIO2 Medical Products, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	238	1,584
Investment, Identifier [Axis]: SVP-Singer Holdings Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	621
Investment, Identifier [Axis]: Salus Workers' Compensation, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	3,102
Investment, Identifier [Axis]: Senior Loan Fund JV I, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	13,125	13,125
Investment, Identifier [Axis]: Sierra Enterprises, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,424	0
Investment, Identifier [Axis]: Sorenson Communications, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	5,409	5,409
Investment, Identifier [Axis]: Spanx, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	2,267	3,092
Investment, Identifier [Axis]: Spruce Bidco I Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	9,271	0
Investment, Identifier [Axis]: SumUp Holdings Luxembourg
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	5,101	5,101
Investment, Identifier [Axis]: Supreme Fitness Group NY Holdings, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	1,552
Investment, Identifier [Axis]: TBRS, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	4,209	0
Investment, Identifier [Axis]: Telephone and Data Systems, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	6,273
Investment, Identifier [Axis]: Telestream 2 LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	745	0
Investment, Identifier [Axis]: Telestream Holdings Corporation
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	0	244
Investment, Identifier [Axis]: Truck-Lite Co., LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	10,259	5,721
Investment, Identifier [Axis]: USIC Holdings, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	1,812	1,938
Investment, Identifier [Axis]: Verona Pharma, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	4,568	14,846
Investment, Identifier [Axis]: WP CPP Holdings, LLC
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	3,272	3,272
Investment, Identifier [Axis]: Whitney Merger Sub, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	2,388	0
Investment, Identifier [Axis]: iCIMs, Inc.
Financial Support for Nonconsolidated Legal Entity [Line Items]
Unfunded commitments	$ 1,545	$ 5,802