Long Term Debt - Credit Facility Narrative (Details)	3 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Apr. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Line of Credit Facility [Line Items]
Outstanding borrowings	$ 400,000,000			$ 400,000,000
Line of Credit | RBL Facility
Line of Credit Facility [Line Items]
Deferred financing costs incurred in connection with securing the RBL Facility	$ 11,700,000
Amortization period	5 years
Interest expense	$ 1,100,000	$ 1,100,000
Outstanding borrowings	0			$ 0
Line of Credit | RBL Facility | Magnolia Operating
Line of Credit Facility [Line Items]
Maximum commitments, aggregate principal amount	1,000,000,000.0
Borrowing base	$ 550,000,000.0
Leverage ratio (less than)	4.00
Leverage ratio, minimum threshold for current ratio	3.00
Current ratio (greater than)	1.00
Line of Credit | RBL Facility | Magnolia Operating | Subsequent Event
Line of Credit Facility [Line Items]
Maximum commitments, aggregate principal amount			$ 450,000,000.0
Line of Credit | Letter of Credit Sublimit | Magnolia Operating
Line of Credit Facility [Line Items]
Maximum commitments, aggregate principal amount	$ 100,000,000.0