Net Assets - Additional Information (Details) - USD ($)				1 Months Ended	3 Months Ended		12 Months Ended		24 Months Ended
	Nov. 02, 2023	Oct. 25, 2021	Dec. 01, 2017	Oct. 31, 2015	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Mar. 24, 2021	Sep. 29, 2021	Feb. 24, 2022	Mar. 31, 2020
Class Of Stock [Line Items]
Common stock, shares authorized					100,000,000		100,000,000
Common stock, par value					$ 0.01		$ 0.01
Stock repurchased during period, shares					871,345		871,345
Stock repurchased during period, value					$ 10,800,000		$ 10,800,000
Stock repurchase program, expiration date	Nov. 02, 2024				Feb. 24, 2023
Stock issued during period, shares, dividend reinvestment plan					20,531	64,214
Stock issued during period, value, dividend reinvestment plan					$ 300,000	$ 800,000
Maximum cost of shares that may be repurchased	$ 25,000,000				25,000,000					$ 25,000,000
Dividends common stock					$ 19,040,000	18,229,000
Repurchase Program
Class Of Stock [Line Items]
Stock repurchased during period, shares					887,096
Stock repurchased during period, value					$ 10,600,000
Dividend Paid
Class Of Stock [Line Items]
Dividends common stock					19,000,000
Dividends Paid In Cash
Class Of Stock [Line Items]
Dividends common stock					18,800,000	17,500,000
Dividends Declared
Class Of Stock [Line Items]
Dividends common stock					$ 19,000,000	$ 18,200,000
R. David Spreng
Class Of Stock [Line Items]
Issuance of common stock, Shares				1,667
Issuance of common stock, value				$ 25,000
Runway Growth Holdings LLC
Class Of Stock [Line Items]
Issuance of common stock, Shares								22,564
Offering price								$ 15			$ 15
Issuance of common stock, value								$ 300,000
IPO
Class Of Stock [Line Items]
Issuance of common stock, Shares		6,850,000
Offering price		$ 14.6
Proceeds from common stock issued		$ 93,000,000
Initial Private Offering
Class Of Stock [Line Items]
Issuance of common stock, Shares			18,241,157
Issuance of common stock, value			$ 275,000,000
Second Private Offering
Class Of Stock [Line Items]
Issuance of common stock, Shares									9,617,379
Issuance of common stock, value									$ 144,300,000
Capital commitments									$ 181,700,000