Ameresco, Inc. Quarterly report [Sections 13 or 15(d)]

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Fair Value of Derivative Instruments on the Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2026	Dec. 31, 2025
Derivatives Designated as Hedging Instruments \| Interest rate swap contracts \| Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherAssetsNoncurrent
Derivatives, Fair Value [Line Items]
Asset derivatives	$ 1,735	$ 721
Derivatives Not Designated as Hedging Instruments \| Interest rate swap contracts \| Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherAssetsNoncurrent
Derivatives, Fair Value [Line Items]
Asset derivatives	1,475	0
Derivatives Not Designated as Hedging Instruments \| Interest rate swap contracts \| Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherLiabilitiesNoncurrent
Derivatives, Fair Value [Line Items]
Liability derivatives	0	197
Derivatives Not Designated as Hedging Instruments \| Make-whole provisions \| Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherLiabilitiesNoncurrent
Derivatives, Fair Value [Line Items]
Liability derivatives	$ 21,027	$ 19,075