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

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

Summary of Significant Accounting Policies- Derivative Financial Instruments (Details) (Interest rate swap instruments, USD $) In Thousands, unless otherwise specified	1 Months Ended	3 Months Ended	1 Months Ended
	Mar. 31, 2010	Jun. 30, 2014	Jul. 31, 2011	Oct. 31, 2012 swap	Dec. 31, 2007 contract	Sep. 30, 2013
Derivative [Line Items]
Number of instruments held (contracts)					2
Interest Rate Swap Contract 1
Derivative [Line Items]
Initial notional amount of interest rate swaps					13,081
Interest rate swaps, variable to fixed interest rates (percent)					5.40%
Interest Rate Swap Contract 2
Derivative [Line Items]
Initial notional amount of interest rate swaps					3,256
Interest rate swaps, variable to fixed interest rates (percent)					5.30%
Interest Rate Swap Contract 3
Derivative [Line Items]
Initial notional amount of interest rate swaps	27,900
Interest rate swaps, variable to fixed interest rates (percent)	6.99%
Term of interest rate swap contract	14 years
Interest Expense Reclassified from Accumulated Other Comprehensive Loss into Other Expenses, Net		566
Interest Rate Swap Contract 4
Derivative [Line Items]
Initial notional amount of interest rate swaps			38,571
Interest rate swaps, variable to fixed interest rates (percent)			1.965%
Term of interest rate swap contract			5 years
Interest Rate Swap Contract 5
Derivative [Line Items]
Number of instruments held (contracts)				2
Initial notional amount of interest rate swaps				16,750
Interest rate swaps, variable to fixed interest rates (percent)				1.71%
Term of interest rate swap contract				8 years
Future increase in notional amount						42,247
Interest Rate Swap Contract 6
Derivative [Line Items]
Number of instruments held (contracts)				2
Initial notional amount of interest rate swaps				$ 25,377
Interest rate swaps, variable to fixed interest rates (percent)				3.70%
Term of interest rate swap contract				8 years