Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2022	Aug. 03, 2022
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q2
Document Quarterly Report	true
Document Transition Report	false
Current Fiscal Year End Date	--12-31
Entity File Number	814-01180
Entity Central Index Key	0001653384
Entity Registrant Name	Runway Growth Finance Corp.
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Common Stock, Shares Outstanding		40,759,727
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Tax Identification Number	47-5049745
Entity Address, Address Line One	205 N. Michigan Ave.
Entity Address, Address Line Two	Suite 4200
Entity Address, City or Town	Chicago
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60601
City Area Code	312
Local Phone Number	281‑6270
Entity Incorporation, State or Country Code	MD
Entity Interactive Data Current	Yes
Common Stock, par value $0.01 per share
Document Information [Line Items]
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	RWAY
Security Exchange Name	NASDAQ
7.50% Notes due 2027
Document Information [Line Items]
Title of 12(b) Security	7.50% Notes due 2027
Trading Symbol	RWAYL
Security Exchange Name	NASDAQ