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

Geographic Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]
Assets	$ 225,144us-gaap_NoncurrentAssets				$ 219,443us-gaap_NoncurrentAssets				$ 225,144us-gaap_NoncurrentAssets	$ 219,443us-gaap_NoncurrentAssets
Revenues	181,061us-gaap_SalesRevenueNet	168,891us-gaap_SalesRevenueNet	142,558us-gaap_SalesRevenueNet	100,731us-gaap_SalesRevenueNet	176,134us-gaap_SalesRevenueNet	161,648us-gaap_SalesRevenueNet	126,253us-gaap_SalesRevenueNet	110,136us-gaap_SalesRevenueNet	593,241us-gaap_SalesRevenueNet	574,171us-gaap_SalesRevenueNet	631,171us-gaap_SalesRevenueNet
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Assets	207,858				201,026				207,858	201,026
Revenues									509,200	501,558	563,746
CANADA
Revenues from External Customers and Long-Lived Assets [Line Items]
Assets	17,145				18,324				17,145	18,324
Revenues									70,069	68,797	60,590
Other Countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Assets	141				93				141	93
Revenues									$ 13,972	$ 3,816	$ 6,835