Cover Page - shares	9 Months Ended
	Sep. 30, 2020	Nov. 02, 2020
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	001-38083
Entity Registrant Name	Magnolia Oil & Gas Corp
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	81-5365682
Entity Address, Address Line One	Nine Greenway Plaza, Suite 1300
Entity Address, City or Town	Houston,
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77046
City Area Code	713
Local Phone Number	842-9050
Title of 12(b) Security	Class A Common Stock, par value $0.0001
Trading Symbol	MGY
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Central Index Key	0001698990
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Amendment Flag	false
Class A Common Stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		165,500,753
Class B Common Stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		85,789,814