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Summary of product warranty activity (Details) (USD $)
|
Dec. 31, 2013
|
Dec. 31, 2012
|
|---|---|---|
| Summary of product warranty activity | ||
| Beginning balance - January 1 | $ 2,671,409 | $ 1,210,909 |
| Additions for current year deliveries | 970,775 | 996,439 |
| Reductions for payments made | (2,034,053) | (2,809,263) |
| Reserve Adjustment | 3,273,324 | |
| Ending balance - December 31 | $ 1,608,131 | $ 2,671,409 |