Summary of Significant Accounting Policies - Additional Information (Details)		1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 31, 2016 USD ($)	Oct. 31, 2021 USD ($)	Mar. 31, 2024 USD ($) Loan shares	Mar. 31, 2023 USD ($) shares	Dec. 31, 2023 USD ($)	Dec. 31, 2019 USD ($)	Mar. 07, 2024 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Amount of equity capital initially committed to provide			$ 235,820,000		$ 201,520,000
Number of loans | Loan			2
PIK Income as a % of net investment income			10.50%	9.70%
Payment of excise tax percentage			4.00%
Percentage of minimum beneficial ownership of voting securities for control			25.00%
Percentage of minimum board representation for control			50.00%
Percentage of beneficial ownership of voting securities for affiliation			5.00%
Potentially dilutive securities outstanding | shares			0	0
Amortized cost basis of financial assets subject to CECL			$ 400,000		2,300,000
CECL reserve			200,000		0
Interest receivable			6,700,000		6,000,000
Other comprehensive income			$ 0	$ 0
ASU 2022-03
Summary Of Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]			true
Change in Accounting Principle, Accounting Standards Update, Adoption Date			Jan. 01, 2024
Cash Equivalents
Summary Of Significant Accounting Policies [Line Items]
Investments in money market funds			$ 6,200,000		0
Joint Venture
Summary Of Significant Accounting Policies [Line Items]
Amount of equity capital initially committed to provide			$ 35,000,000		0
Joint Venture | Runway-Cadma I LLC
Summary Of Significant Accounting Policies [Line Items]
Amount of equity capital initially committed to provide							$ 35,000,000
Ownership percentage			50.00%
Joint Venture | Runway-Cadma I LLC | Cadma Capital Partners LLC
Summary Of Significant Accounting Policies [Line Items]
Amount of equity capital initially committed to provide							$ 35,000,000
Ownership percentage			50.00%
Second Private Offering
Summary Of Significant Accounting Policies [Line Items]
Offering cost excluding placement agent fees						$ 600,000
Placement agent fees						200,000
Offering cost						700,000
IPO
Summary Of Significant Accounting Policies [Line Items]
Offering cost		$ 7,000,000
Minimum | Initial Private Offering | Runway Growth Holdings LLC
Summary Of Significant Accounting Policies [Line Items]
Adjustment to additional paid in capital stock issued issuance costs	$ 1,000,000
Maximum | Second Private Offering
Summary Of Significant Accounting Policies [Line Items]
Offering cost						$ 600,000
Maximum | Initial Private Offering
Summary Of Significant Accounting Policies [Line Items]
Adjustment to additional paid in capital stock issued issuance costs	$ 1,000,000
Mingle Healthcare Solutions Inc
Summary Of Significant Accounting Policies [Line Items]
Write off accrued and uncollected paid in kind interest			$ 0		$ 0
Number of loans | Loan			1
Aggregate principal funded on non-accrual status			$ 5,000,000
Fair value on non-accrual status			$ 3,200,000
Percentage of investment portfolio on non-accrual status			3.80%
Mingle Healthcare Solutions Inc | Cash Interest Income
Summary Of Significant Accounting Policies [Line Items]
Cumulative interest on investments			$ 200,000
Snagajob, Inc.
Summary Of Significant Accounting Policies [Line Items]
Aggregate principal funded on non-accrual status			42,700,000
Fair value on non-accrual status			35,500,000
Snagajob, Inc. | Cash Interest Income
Summary Of Significant Accounting Policies [Line Items]
Cumulative interest on investments			$ 200,000