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Business Acquisitions and Related Transactions - Results of Acquired Companies (Details) (USD $)
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3 Months Ended | 6 Months Ended | ||
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Jun. 30, 2012
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Jun. 30, 2011
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Jun. 30, 2012
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Jun. 30, 2011
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| Business Acquisition [Line Items] | ||||
| Revenue | $ 164,099,905 | $ 165,481,943 | $ 310,673,274 | $ 311,901,712 |
| Pre-tax income (loss) | 7,195,498 | 12,368,994 | 9,282,683 | 19,771,947 |
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AEG [Member]
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| Business Acquisition [Line Items] | ||||
| Revenue | 4,647,487 | 8,700,250 | ||
| Pre-tax income (loss) | 849,515 | 647,937 | ||
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Ameresco Southwest [Member]
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| Business Acquisition [Line Items] | ||||
| Revenue | 11,933,860 | 23,390,954 | ||
| Pre-tax income (loss) | 934,380 | 1,271,517 | ||
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AIS [Member]
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| Business Acquisition [Line Items] | ||||
| Revenue | 2,856,687 | 6,016,672 | ||
| Pre-tax income (loss) | $ (21,580) | $ 40,215 | ||