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

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income tax (benefit) provision	$ (1,192)	$ 3,100	$ (883)	$ 597
Effective tax rate, percentage	(6.20%)	14.90%	(1.80%)	1.80%
Unrecognized tax benefits	$ 400		$ 400		$ 190

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.