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

Commitments and Contingencies - Additional Information (Details) In Thousands, unless otherwise specified	12 Months Ended			1 Months Ended	3 Months Ended	1 Months Ended
	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Oct. 31, 2012 Unfavorable Regulatory Action	Dec. 31, 2014 Unfavorable Regulatory Action	Oct. 31, 2012 Maximum Unfavorable Regulatory Action	Jun. 30, 2014 EEX USD ($)	Jun. 30, 2014 EEX GBP (£)
Loss Contingencies [Line Items]
Operating Leases, Rent Expense, Net	$ 5,667us-gaap_OperatingLeasesRentExpenseNet	$ 4,947us-gaap_OperatingLeasesRentExpenseNet	$ 5,031us-gaap_OperatingLeasesRentExpenseNet
Anti-dumping duty rate						249.96%
Countervailing duty rate, prior to increase				3.61%
Countervailing duty rate				15.24%	31.18%
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High							$ 6,989,000	£ 4,500