Annual report pursuant to Section 13 and 15(d)

Income Taxes - Reconciliation of effective tax rates (Details)

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Income Taxes - Reconciliation of effective tax rates (Details) (USD $)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Income Tax Disclosure [Abstract]      
Income before provision for income taxes $ 2,758,868 $ 24,606,886 $ 44,180,105
Federal statutory tax expense 965,604 8,612,410 15,463,037
State income taxes, net of federal benefit 200,981 817,901 1,553,018
Net state impact of deferred rate change (69,342) 0 (259,339)
Non deductible expenses 2,007,657 2,611,576 115,629
Stock-based compensation expense 373,398 336,564 240,557
Energy efficiency preferences (3,556,074) (7,032,798) (6,247,283)
Foreign items and rate differential 348,891 557,104 239,692
Miscellaneous 73,566 343,996 (338,139)
Income tax (benefit) provision $ 344,681 $ 6,246,753 $ 10,767,172
Effective tax rate:      
Federal statutory rate expense 35.00% 35.00% 35.00%
State income taxes, net of federal benefit 7.30% 3.30% 3.50%
Net state impact of deferred rate change (2.50%) 0.00% (0.60%)
Non deductible expenses 72.80% 10.60% 0.30%
Stock-based compensation expense 13.50% 1.40% 0.50%
Energy efficiency preferences (128.90%) (28.60%) (14.10%)
Foreign items and rate differential 12.60% 2.30% 0.50%
Miscellaneous 2.70% 1.40% (0.70%)
Effective tax rate 12.50% 25.40% 24.40%