Significant Accounting Policies - Schedule of Wholly Owned Subsidiaries Included in Consolidated Financial Statements (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
4Front Holdings LLC
Subsidiary Or Equity Method Investee [Line Items]
Business Name	4Front Holdings, LLC
Entity Type	Holding Company
State of Operations	DE
Ownership %	100.00%	100.00%
4Front Advisors, LLC
Subsidiary Or Equity Method Investee [Line Items]
Business Name	4Front Advisors, LLC
Entity Type	Consulting Company
State of Operations	AZ
Ownership %	100.00%	100.00%
Mission Partners USA, LLC
Subsidiary Or Equity Method Investee [Line Items]
Business Name	Mission Partners USA, LLC
Entity Type	Investment Company
State of Operations	DE
Ownership %	100.00%	100.00%
Linchpin Investors, LLC
Subsidiary Or Equity Method Investee [Line Items]
Business Name	Linchpin Investors, LLC
Entity Type	Finance Company
State of Operations	DE
Ownership %	100.00%	100.00%
Healthy Pharms Inc.
Subsidiary Or Equity Method Investee [Line Items]
Business Name	Healthy Pharms Inc.
Entity Type	Collocated Cultivation / Production / Dispensary
State of Operations	MA
Ownership %	100.00%	100.00%
MMA Capital, LLC
Subsidiary Or Equity Method Investee [Line Items]
Business Name	MMA Capital, LLC
Entity Type	Finance Company
State of Operations	MA
Ownership %	95.00%	85.30%
IL Grown Medicine, LLC
Subsidiary Or Equity Method Investee [Line Items]
Business Name	IL Grown Medicine, LLC
Entity Type	Cultivation
State of Operations	IL
Ownership %	100.00%	100.00%
Harborside Illinois Grown Medicine, Inc.
Subsidiary Or Equity Method Investee [Line Items]
Business Name	Harborside Illinois Grown Medicine, Inc.
Entity Type	Dispensary (allowing for the operation of 2 dispensaries)
State of Operations	IL
Ownership %	100.00%	100.00%
Om of Medicine LLC
Subsidiary Or Equity Method Investee [Line Items]
Business Name	Om of Medicine, LLC
Entity Type	Co-located Medical Provisioning Center (Dispensary); Co-located Adult-Use Dispensary
State of Operations	MI
Ownership %	100.00%	100.00%
Mission MA, Inc.
Subsidiary Or Equity Method Investee [Line Items]
Business Name	Mission MA, Inc.
Entity Type	Collocated Cultivation / Production / Dispensary
State of Operations	MA
Ownership %	100.00%	100.00%
Real Estate Properties LLC
Subsidiary Or Equity Method Investee [Line Items]
Business Name	Real Estate Properties LLC
Entity Type	Real Estate Holding
State of Operations	WA
Ownership %	100.00%	100.00%
Fuller Hill Development Co, LLC
Subsidiary Or Equity Method Investee [Line Items]
Business Name	Fuller Hill Development Co, LLC
Entity Type	Real Estate Holding
State of Operations	WA
Ownership %	100.00%	100.00%
Ag-Grow Imports LLC
Subsidiary Or Equity Method Investee [Line Items]
Business Name	Ag-Grow Imports LLC
Entity Type	Importer of Equipment
State of Operations	WA
Ownership %	100.00%	100.00%
Pure Ratios Holdings, Inc.
Subsidiary Or Equity Method Investee [Line Items]
Business Name	Pure Ratios Holdings, Inc.
Entity Type	Online CBD Retail
State of Operations	DE
Ownership %	100.00%	100.00%
4Front California Capital Holdings Inc.
Subsidiary Or Equity Method Investee [Line Items]
Business Name	4Front California Capital Holdings Inc.
Entity Type	Real Estate Holding
State of Operations	CA
Ownership %	100.00%	100.00%
4Front Nevada Corp.
Subsidiary Or Equity Method Investee [Line Items]
Business Name	4Front Nevada Corp.
Entity Type	Holding Company
State of Operations	NV
Ownership %	100.00%	100.00%
Brightleaf Development LLC
Subsidiary Or Equity Method Investee [Line Items]
Business Name	Brightleaf Development LLC
Entity Type	Holding Company
State of Operations	WA
Ownership %	100.00%	100.00%
Mission Partners IP, LLC
Subsidiary Or Equity Method Investee [Line Items]
Business Name	Mission Partners IP, LLC
Entity Type	IP Holding Company
State of Operations	DE
Ownership %	100.00%	100.00%
4Front US Holdings, Inc.
Subsidiary Or Equity Method Investee [Line Items]
Business Name	4Front US Holdings, Inc.
Entity Type	Holding Company
State of Operations	DE
Ownership %	100.00%	100.00%
4Front Management Associates, LLC
Subsidiary Or Equity Method Investee [Line Items]
Business Name	4Front Management Associates, LLC
Entity Type	Management Company
State of Operations	MA
Ownership %	95.00%	76.00%
4Front Ventures Corp.
Subsidiary Or Equity Method Investee [Line Items]
Business Name	4Front Ventures Corp.
Entity Type	Holding Company
State of Operations	Canada
Ownership %	100.00%	100.00%