Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Mar. 04, 2021	Jun. 30, 2020
Document Information [Line Items]
Entity Registrant Name	Falcon Minerals Corp
Entity Central Index Key	0001703785
Amendment Flag	true
Current Fiscal Year End Date	--12-31
Document Type	10-K/A
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
ICFR Auditor Attestation Flag	false
Entity Public Float			$ 157.1
Entity File Number	001-38158
Entity Tax Identification Number	82-0820780
Entity Address, Address Line One	510 Madison Avenue
Entity Address, Address Line Two	8th Floor
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10022
City Area Code	212
Local Phone Number	506-5925
Entity Interactive Data Current	Yes
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false
Amendment Description	On May 4, 2021, the Audit Committee (the “Audit Committee”) of the Board of Directors and in consultation with management, concluded that its audited consolidated financial statements for the years ended December 31, 2020, 2019 and 2018, and the interim period within those years, could no longer be relied upon as a result of material accounting errors identified by management.
Documents Incorporated by Reference	Portions of the proxy statement for registrant’s 2021 Annual Meeting of Stockholders are incorporated by reference in Part III in this Form 10-K.
Class A common stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		46,107,183
Title of 12(b) Security	Class A Common Stock, par value $0.0001 per share
Trading Symbol	FLMN
Security Exchange Name	NASDAQ
Class C common stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		40,000,000
Warrants [Member]
Document Information [Line Items]
Title of 12(b) Security	Warrants, each to purchase one share of Class A Common Stock
Trading Symbol	FLMNW
Security Exchange Name	NASDAQ