Ameresco, Inc. Quarterly report pursuant to Section 13 or 15(d)

Leases - Additional Information (Details)

Leases - Additional Information (Details)	3 Months Ended		9 Months Ended
Leases - Additional Information (Details)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) project	Sep. 30, 2020 USD ($)	Dec. 31, 2021 USD ($)	Jul. 31, 2021 USD ($)	Mar. 22, 2021 USD ($)	Dec. 31, 2020 USD ($)	Aug. 31, 2018 USD ($)
Lessee, Lease, Description [Line Items]
Commitment, amount	$ 3,320,000		$ 3,320,000
Net amortization expense	57,000	$ 57,000	$ 172,000	$ 170,000
August 2018 Long Term Finance Liability
Lessee, Lease, Description [Line Items]
Maximum combined funding amount							$ 350,000,000		$ 150,000,000
December 2020 Long Term Finance Liability
Lessee, Lease, Description [Line Items]
Maximum combined funding amount						$ 23,559,000		$ 4,500,000
Solar Photovoltaic Projects \| August 2018 Long Term Finance Liability
Lessee, Lease, Description [Line Items]
Solar PV projects sold \| project			3
Investment fund call option exercise			$ 31,095,000
Solar Photovoltaic Projects \| December 2020 Long Term Finance Liability
Lessee, Lease, Description [Line Items]
Solar PV projects sold \| project			1
Investment fund call option exercise			$ 3,281,000
Solar Photovoltaic Projects \| Revolving Credit Facility \| Line of Credit \| August 2018 Long Term Finance Liability
Lessee, Lease, Description [Line Items]
Available funding under lending commitment	280,610,000		280,610,000
Solar Photovoltaic Projects \| Revolving Credit Facility \| Line of Credit \| December 2020 Long Term Finance Liability
Lessee, Lease, Description [Line Items]
Available funding under lending commitment	$ 15,936,000		$ 15,936,000
Forecast
Lessee, Lease, Description [Line Items]
Commitment, amount					$ 3,000,000