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Warranty (Details) (USD $)
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Warranty    
Period of warranties, low end of the range 90 days  
Period of warranties, high end of the range 1 year  
Warranty provisions and claims for the years    
Beginning balance $ 240,621 $ 205,506
Warranty provisions 122,889 35,826
Warranty claims (118,241) (61,007)
Ending balance $ 245,269 $ 180,325