Ameresco, Inc. Annual report pursuant to Section 13 and 15(d)

Leases - Narrative (Details)

Leases - Narrative (Details)	12 Months Ended
Leases - Narrative (Details)	Dec. 31, 2019 USD ($) project	Dec. 31, 2018 USD ($) project	Dec. 31, 2017 USD ($) project	Jan. 31, 2020 USD ($)	Aug. 31, 2019 USD ($)	Jul. 31, 2019	Jan. 01, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease assets	$ 32,791,000						$ 31,639,000
Current portions of operating lease liabilities	5,802,000						5,084,000
Long-term portions of operating lease liabilities	29,101,000						28,480,000
Operating leases, rent expense	8,179,000	$ 6,463,000	$ 6,362,000
Maximum combined funding amount					$ 100,000,000
Proceeds from sale-leaseback financings	0	$ 5,145,000	$ 51,204,000
Available funding under lending commitment	$ 81,000,000
Minimum
Lessee, Lease, Description [Line Items]
Operating lease renewal term	6 months
Maximum
Lessee, Lease, Description [Line Items]
Operating lease renewal term	7 years
Solar PV project
Lessee, Lease, Description [Line Items]
Number of projects sold then leased back to separate investor \| project		2	1
Solar PV projects sold \| project	3	2	13
Proceeds from sale-leaseback financings	$ 13,700,000
Long Term Financing Facility
Lessee, Lease, Description [Line Items]
Stated interest rate (percent)						0.28%
Long Term Financing Facility \| Minimum
Lessee, Lease, Description [Line Items]
Stated interest rate (percent)	0.00%
Long Term Financing Facility \| Maximum
Lessee, Lease, Description [Line Items]
Stated interest rate (percent)	0.28%
Subsequent Event
Lessee, Lease, Description [Line Items]
Maximum combined funding amount				$ 150,000,000
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Operating lease assets							31,639,000
Current portions of operating lease liabilities							5,084,000
Long-term portions of operating lease liabilities							$ 28,480,000