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

Geographic Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
Geographic Information (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 466,937				$ 361,746				$ 466,937	$ 361,746
Revenues	217,371	$ 205,375	$ 196,982	$ 167,410	211,133	$ 204,744	$ 166,665	$ 134,610	787,138	717,152	$ 651,227
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	443,385				343,344				443,385	343,344
Revenues									734,748	665,793	588,791
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	22,107				17,082				22,107	17,082
Revenues									36,728	42,186	49,706
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 1,445				$ 1,320				1,445	1,320
Revenues									$ 15,662	$ 9,173	$ 12,730