Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2021	Apr. 11, 2022
Document Information [Line Items]
Entity Registrant Name	4Front Ventures Corp.
Document Type	10-K
Current Fiscal Year End Date	--12-31
Amendment Flag	false
Entity Central Index Key	0001783875
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Document Period End Date	Dec. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Shell Company	false
Entity Ex Transition Period	false
Document Annual Report	true
Document Transition Report	false
Entity File Number	000-56075
Entity Incorporation, State or Country Code	OR
Entity Interactive Data Current	Yes
Entity Common Stock, Shares Outstanding		627,826,303
Entity Address, Address Line One	5060 N. 40th Street
Entity Address, Address Line Two	Suite 120
Entity Address, City or Town	Phoenix
Entity Address, State or Province	AZ
Entity Address, Postal Zip Code	85018
City Area Code	602
Local Phone Number	633-3067
Entity Tax Identification Number	26-1449404
Trading Symbol	FFNT
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
ICFR Auditor Attestation Flag	false
Entity Public Float	$ 598,834,450
Auditor Name	Davidson & Company LLP
Auditor Firm ID	731
Auditor Location	Vancouver, British Columbia, Canada
Class A Subordinate Voting Share [Member]
Document Information [Line Items]
Trading Symbol	FFNTF
Title of 12(b) Security	Class A Subordinate Voting Shares, no par value