Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Earnings Per Share (Details)

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Summary of Significant Accounting Policies - Earnings Per Share (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Accounting Policies [Abstract]                      
Deferred financing fees, net $ 5,303       $ 4,313       $ 5,303 $ 4,313  
Net income attributable to Ameresco, Inc.                 $ 2,977 $ 10,383 $ 2,414
Basic weighted-average shares outstanding 46,556,977 46,517,638 46,493,162 46,408,123 46,350,835 46,315,968 46,064,049 45,909,995 46,494,448 46,161,846 45,560,078
Effect of dilutive securities:                      
Stock options (in shares)                 1,170,447 865,909 1,125,047
Diluted weighted-average shares outstanding (in shares) 48,011,302 48,056,359 47,385,412 46,408,123 47,326,417 47,308,414 46,904,199 45,909,995 47,664,895 47,027,755 46,685,125
Stock options excluded from calculation of dilutive shares as the effect would be anti-dilutive (in shares)                 1,767,778 1,737,261 1,856,591