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

Goodwill and Intangible Assets Goodwill and Intangible Assets - Amortization (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 4,738us-gaap_AmortizationOfIntangibleAssets	$ 4,802us-gaap_AmortizationOfIntangibleAssets	$ 5,282us-gaap_AmortizationOfIntangibleAssets
Customer contracts
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	1,673	1,550	2,450
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	1,688	1,643	1,265
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	805	968	724
Technology
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	490	517	671
Trade names
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 82	$ 124	$ 172