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Income Taxes - Reconciliation of effective tax rates (Details) (USD $)
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3 Months Ended | 12 Months Ended | |||||||||||||
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Dec. 31, 2012
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Sep. 30, 2012
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Jun. 30, 2012
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Mar. 31, 2012
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Dec. 31, 2011
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Sep. 30, 2011
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Jun. 30, 2011
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Mar. 31, 2011
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Dec. 31, 2010
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Sep. 30, 2010
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Jun. 30, 2010
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Mar. 31, 2010
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Dec. 31, 2012
Rate
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Dec. 31, 2011
Rate
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Dec. 31, 2010
Rate
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| Income Tax Disclosure [Abstract] | |||||||||||||||
| Income before provision for income taxes | $ 6,048 | $ 9,396 | $ 6,846 | $ 2,317 | $ 10,868 | $ 13,713 | $ 11,927 | $ 7,672 | $ 12,688 | $ 16,162 | $ 9,643 | $ 1,207 | $ 24,606,886 | $ 44,180,105 | $ 39,699,301 |
| Federal statutory tax expense | 8,612,410 | 15,463,037 | 13,894,755 | ||||||||||||
| State income taxes, net of federal benefit | 817,901 | 1,553,018 | 1,220,197 | ||||||||||||
| Net state impact of deferred rate change | 0 | (259,339) | 0 | ||||||||||||
| Non deductible expenses | 2,611,576 | 115,629 | 99,128 | ||||||||||||
| Stock-based compensation expense | 336,564 | 240,557 | 12,132 | ||||||||||||
| Energy efficiency preferences | (7,032,798) | (6,247,283) | (4,246,589) | ||||||||||||
| Foreign items and rate differential | 557,104 | 239,692 | (70,656) | ||||||||||||
| Miscellaneous | 343,996 | (338,139) | 1,276,668 | ||||||||||||
| Income tax (benefit) provision | $ 954 | $ 2,684 | $ 2,027 | $ 582 | $ 2,425 | $ 2,690 | $ 3,537 | $ 2,115 | $ 3,805 | $ 4,862 | $ 3,089 | $ 429 | $ 6,246,753 | $ 10,767,172 | $ 12,185,635 |
| Effective tax rate: | |||||||||||||||
| Federal statutory rate expense | 35.00% | 35.00% | 35.00% | ||||||||||||
| State income taxes, net of federal benefit | 3.30% | 3.50% | 3.10% | ||||||||||||
| Net state impact of deferred rate change | 0.00% | (0.60%) | 0.00% | ||||||||||||
| Non deductible expenses | 10.60% | 0.30% | 0.30% | ||||||||||||
| Stock-based compensation expense | 1.40% | 0.50% | 0.00% | ||||||||||||
| Energy efficiency preferences | (28.60%) | (14.10%) | (10.70%) | ||||||||||||
| Foreign items and rate differential | 2.30% | 0.50% | (0.20%) | ||||||||||||
| Miscellaneous | 1.40% | (0.70%) | 3.20% | ||||||||||||
| Effective tax rate | 25.40% | 24.40% | 30.70% | ||||||||||||
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- Definition
Effective Income Tax Rate Reconciliation, Energy Efficiency Preferences No definition available.
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- Definition
Effective Income Tax Rate Reconciliation, State Impact of Deferred Rate Change, Net No definition available.
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- Definition
Income Tax Reconciliation, Nondeductible Expense, Deffered Rate Change, Net No definition available.
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- Definition
Income Tax Reconciliation Nondeductible Expense Energy Efficiency Preferences No definition available.
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- Definition
Income Tax Reconciliation, Nondeductible Expense, Miscellaneous No definition available.
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- Definition
A ratio calculated by dividing the reported amount of income tax expense attributable to continuing operations for the period by GAAP-basis pretax income from continuing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Details
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- Definition
The domestic federal statutory tax rate applicable under enacted tax laws to the Company's pretax income from continuing operations for the period. The "statutory" tax rate is the regular tax rate if there are alternative tax systems. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by the difference between statutory income tax rates in foreign jurisdictions and the domestic federal statutory income tax rate recorded during the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to nondeductible meals and entertainment expenses under enacted tax laws. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to differences in the deductibility or nondeductibility of incentive stock options and other equity-based compensation costs in accordance with generally accepted accounting principles and enacted tax laws. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to all other items not otherwise listed in the existing taxonomy. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by the state and local income tax expense or benefit, net of the federal tax benefit (expense) thereon, recorded during the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investments, income taxes, extraordinary items, and noncontrolling interest. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Details
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- Definition
The sum of the current income tax expense or benefit and the deferred income tax expense or benefit pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The portion of the difference, between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations, that is attributable to total foreign income tax expense or benefit. The foreign income tax expense or benefit difference represents the income tax expense or benefit at applicable domestic statutory income tax rates applied to foreign earnings or loss for the period versus the foreign income tax expense or benefit calculated by applying the appropriate foreign tax rates. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Definition
The portion of the difference between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to nondeductible meal and entertainment expenses under enacted tax laws. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Definition
The portion of the difference between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to differences in the deductibility of incentive stock options and other equity-based compensation costs in accordance with generally accepted accounting principles and enacted tax laws. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Definition
The portion of the difference, between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations, that is attributable to state and local income tax expense or benefit. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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