Annual report pursuant to Section 13 and 15(d)

Document Entity Information

Document Entity Information (USD $)
12 Months Ended
Dec. 31, 2011
Jun. 30, 2011
Feb. 29, 2012
Common Class A [Member]
Feb. 29, 2012
Common Class B [Member]
Entity Registrant Name Ameresco, Inc.      
Entity Central Index Key 0001488139      
Current Fiscal Year End Date --12-31      
Entity Filer Category Non-accelerated Filer      
Document Type 10-K      
Document Period End Date Dec. 31, 2011      
Document Fiscal Year Focus 2011      
Document Fiscal Period Focus FY      
Amendment Flag false      
Common Stock     26,119,303 18,000,000
Entity Well-known Seasoned Issuer No      
Entity Voluntary Filers No      
Entity Current Reporting Status Yes      
Entity Public Float   $ 261,384,520