Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Goodwill and Intangible Assets (Details)

v2.4.1.9
Summary of Significant Accounting Policies - Goodwill and Intangible Assets (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 12 Months Ended 1 Months Ended
Sep. 30, 2012
Agreement
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Jul. 31, 2012
Jun. 30, 2013
Feb. 28, 2013
Dec. 31, 2011
Goodwill [Line Items]                
Impairment of goodwill   $ 0us-gaap_GoodwillImpairmentLoss $ 0us-gaap_GoodwillImpairmentLoss $ 1,016us-gaap_GoodwillImpairmentLoss        
Goodwill recorded for acquisitions   60,479us-gaap_Goodwill 53,074us-gaap_Goodwill 48,969us-gaap_Goodwill        
Number of purchase agreements 2amrc_NumberOfPurchaseAgreements              
ESP                
Goodwill [Line Items]                
Business Acquisition, Cost of Acquired Entity, Security Deposit in Escrow           778amrc_BusinessAcquisitionCostOfAcquiredEntitySecurityDepositInEscrow
/ us-gaap_BusinessAcquisitionAxis
= amrc_ESPMember 		   
Goodwill recorded for acquisitions     3,682us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= amrc_ESPMember 		    2,632us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= amrc_ESPMember 		   
Ennovate                
Goodwill [Line Items]                
Business Acquisition, Cost of Acquired Entity, Security Deposit in Escrow             1,200amrc_BusinessAcquisitionCostOfAcquiredEntitySecurityDepositInEscrow
/ us-gaap_BusinessAcquisitionAxis
= amrc_EnnovateMember 		 
Goodwill recorded for acquisitions           1,050us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= amrc_EnnovateMember 		   
FAME                
Goodwill [Line Items]                
Payments to Acquire Businesses, Gross         4,487us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_BusinessAcquisitionAxis
= amrc_FameFacilitySoftwareSolutionsIncMember 		     
Business Acquisition, Cost of Acquired Entity, Security Deposit in Escrow         900amrc_BusinessAcquisitionCostOfAcquiredEntitySecurityDepositInEscrow
/ us-gaap_BusinessAcquisitionAxis
= amrc_FameFacilitySoftwareSolutionsIncMember 		     
Goodwill recorded for acquisitions       1,887us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= amrc_FameFacilitySoftwareSolutionsIncMember 		      1,887us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= amrc_FameFacilitySoftwareSolutionsIncMember
Percentage of stock acquired 100.00%amrc_CapitalStockAcquiredPercentage
/ us-gaap_BusinessAcquisitionAxis
= amrc_FameFacilitySoftwareSolutionsIncMember 		             
AEG                
Goodwill [Line Items]                
Goodwill recorded for acquisitions               8,728us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= amrc_AppliedEnergyGroupIncMember
Percentage of stock acquired 100.00%amrc_CapitalStockAcquiredPercentage
/ us-gaap_BusinessAcquisitionAxis
= amrc_AppliedEnergyGroupIncMember 		             
Ameresco Southwest                
Goodwill [Line Items]                
Goodwill recorded for acquisitions               16,545us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= amrc_AmerescoSouthwestMember
AIS                
Goodwill [Line Items]                
Goodwill recorded for acquisitions               $ 1,549us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= amrc_AmerescoIntelligentSystemsLlcMember
Minimum                
Goodwill [Line Items]                
Intangible assets amortization period   1 year            
Maximum                
Goodwill [Line Items]                
Intangible assets amortization period   15 years