Ameresco, Inc. Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Energy Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Accounting Policies [Abstract]
Interest costs capitalized	$ 994	$ 1,159
Minimum qualifying operating period for prorated repayments of grants	5 years
Deferred grant income	$ 7,050		$ 7,188

Amount of unearned revenue or income classified as other, expected to be taken into income after one year or the normal operating cycle, if longer.