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

Summary of Significant Accounting Policies - Derivative Financial Instruments (Details)

Summary of Significant Accounting Policies - Derivative Financial Instruments (Details) (USD $)	3 Months Ended	1 Months Ended			12 Months Ended
	Jun. 30, 2014	Mar. 31, 2010 swap	Jul. 31, 2011 swap	Oct. 31, 2012 swap	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2007 contract	Sep. 30, 2013
Derivative [Line Items]
Interest Expense Reclassified from Accumulated Other Comprehensive (Loss) Income, Net into Other Expenses, Net	$ 566,000
Interest Rate Swap
Derivative [Line Items]
Number of instruments								2
Interest Rate Swap \| Interest Rate Swap Contract 1
Derivative [Line Items]
Notional amount								13,081,000
Interest rate swaps, variable to fixed interest rates								5.40%
Interest Rate Swap \| Interest Rate Swap Contract 2
Derivative [Line Items]
Notional amount								3,256,000
Interest rate swaps, variable to fixed interest rates								5.30%
Interest Rate Swap \| Interest Rate Swap Contract 3
Derivative [Line Items]
Number of instruments		1
Term of interest rate swap contract		14 years
Notional amount		27,900,000
Interest rate swaps, variable to fixed interest rates		6.99%
Interest Rate Swap \| Interest Rate Swap Contract 4
Derivative [Line Items]
Number of instruments			1
Term of interest rate swap contract			5 years
Notional amount			38,571,000
Interest rate swaps, variable to fixed interest rates			1.965%
Interest Rate Swap \| Interest Rate Swap Contract 5
Derivative [Line Items]
Number of instruments				2
Term of interest rate swap contract				8 years
Notional amount				16,750,000
Interest rate swaps, variable to fixed interest rates				1.71%
Future Increase in Notional Amount									42,247,000
Interest Rate Swap \| Interest Rate Swap Contract 6
Derivative [Line Items]
Number of instruments				2
Term of interest rate swap contract				8 years
Notional amount				25,377,000
Interest rate swaps, variable to fixed interest rates				3.70%
Not Designated as Hedging Instrument \| Interest Rate Swap
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivative					$ 0	$ (266,000)	$ 98,000