Fair Value Measurements - Fair value measurements of investments and foreign currency forward contracts, by major class according to the fair value hierarchy (Details) - USD ($) $ in Thousands	Mar. 31, 2024		Dec. 31, 2023
Fair Value Measurements
Total investments	$ 2,814,217	[1],[2]	$ 2,528,167	[3],[4]
Senior secured loans
Fair Value Measurements
Total investments	2,432,957		2,171,243
Unitranche secured loans
Fair Value Measurements
Total investments	174,337		184,853
Junior secured loans
Fair Value Measurements
Total investments	102,443		87,986
Equity securities
Fair Value Measurements
Total investments	104,480		84,085
Fair Value, Recurring
Fair Value Measurements
Total investments	2,814,217		2,528,167
Fair Value, Recurring | Forward Contracts
Fair Value Measurements
Foreign currency forward contracts asset (liability)	(734)		(3,087)
Fair Value, Recurring | Senior secured loans
Fair Value Measurements
Total investments	2,432,957		2,171,243
Fair Value, Recurring | Unitranche secured loans
Fair Value Measurements
Total investments	174,337		184,853
Fair Value, Recurring | Junior secured loans
Fair Value Measurements
Total investments	102,443		87,986
Fair Value, Recurring | Equity securities
Fair Value Measurements
Total investments	104,480		84,085
Fair Value, Recurring | Level 1
Fair Value Measurements
Total investments	181		23
Fair Value, Recurring | Level 1 | Forward Contracts
Fair Value Measurements
Foreign currency forward contracts asset (liability)	0		0
Fair Value, Recurring | Level 1 | Senior secured loans
Fair Value Measurements
Total investments	0		0
Fair Value, Recurring | Level 1 | Unitranche secured loans
Fair Value Measurements
Total investments	0		0
Fair Value, Recurring | Level 1 | Junior secured loans
Fair Value Measurements
Total investments	0		0
Fair Value, Recurring | Level 1 | Equity securities
Fair Value Measurements
Total investments	181		23
Fair Value, Recurring | Level 2
Fair Value Measurements
Total investments	0		0
Fair Value, Recurring | Level 2 | Forward Contracts
Fair Value Measurements
Foreign currency forward contracts asset (liability)	(734)		(3,087)
Fair Value, Recurring | Level 2 | Senior secured loans
Fair Value Measurements
Total investments	0		0
Fair Value, Recurring | Level 2 | Unitranche secured loans
Fair Value Measurements
Total investments	0		0
Fair Value, Recurring | Level 2 | Junior secured loans
Fair Value Measurements
Total investments	0		0
Fair Value, Recurring | Level 2 | Equity securities
Fair Value Measurements
Total investments	0		0
Fair Value, Recurring | Level 3
Fair Value Measurements
Total investments	2,814,036		2,528,144
Fair Value, Recurring | Level 3 | Forward Contracts
Fair Value Measurements
Foreign currency forward contracts asset (liability)	0		0
Fair Value, Recurring | Level 3 | Senior secured loans
Fair Value Measurements
Total investments	2,432,957		2,171,243
Fair Value, Recurring | Level 3 | Unitranche secured loans
Fair Value Measurements
Total investments	174,337		184,853
Fair Value, Recurring | Level 3 | Junior secured loans
Fair Value Measurements
Total investments	102,443		87,986
Fair Value, Recurring | Level 3 | Equity securities
Fair Value Measurements
Total investments	$ 104,299		$ 84,062

[1] All of the Company’s investments are issued by eligible portfolio companies, as defined in the Investment Company Act of 1940, as amended, (the “1940 Act”), unless otherwise noted. All of the Company’s investments are issued by U.S. portfolio companies unless otherwise noted.

[2] Except as otherwise noted, because there is no readily available market value for these investments, the fair value of each of these investments is determined in good faith using significant unobservable inputs by the Valuation Designee. (See Note 4 in the accompanying notes to the consolidated financial statements).

[3] All of the Company's investments are issued by eligible portfolio companies, as defined in the Investment Company Act of 1940, as amended, (the “1940 Act”), unless otherwise noted. All of the Company's investments are issued by U.S. portfolio companies unless otherwise noted.

[4] Except as otherwise noted, because there is no readily available market value for these investments, the fair value of each of these investments is determined in good faith using significant unobservable inputs by the Valuation Designee. (See Note 4 in the accompanying notes to the consolidated financial statements.)