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

Business Segment Information - Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue from External Customer [Line Items]
Revenues	$ 211,133	$ 204,744	$ 166,665	$ 134,610	$ 174,225	$ 180,598	$ 162,628	$ 133,776	$ 717,152	$ 651,227	$ 630,832
Project
Revenue from External Customer [Line Items]
Revenues									506,550	454,200	434,380
Energy Assets
Revenue from External Customer [Line Items]
Revenues									69,241	64,882	55,130
Operations and Maintenance
Revenue from External Customer [Line Items]
Revenues									60,574	63,082	59,117
Integrated-PV
Revenue from External Customer [Line Items]
Revenues									38,796	29,325	40,070
Other services
Revenue from External Customer [Line Items]
Revenues									$ 41,991	$ 39,738	$ 42,135