Annual report pursuant to Section 13 and 15(d)

Document and Entity Information

Document and Entity Information (USD $)
12 Months Ended
Dec. 31, 2012
Jun. 29, 2012
Mar. 01, 2013
Class A Common Stock
Mar. 01, 2013
Class B Common Stock
Entity Information [Line Items]        
Entity Registrant Name Ameresco, Inc.      
Entity Central Index Key 0001488139      
Current Fiscal Year End Date --12-31      
Entity Filer Category Accelerated Filer      
Document Type 10-K      
Document Period End Date Dec. 31, 2012      
Document Fiscal Year Focus 2012      
Document Fiscal Period Focus FY      
Amendment Flag false      
Common Stock     27,329,454 18,000,000
Entity Well-known Seasoned Issuer No      
Entity Voluntary Filers No      
Entity Current Reporting Status Yes      
Entity Public Float   $ 241,830,692