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Summary of Warrant Activity (Detail)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Shares    
Beginning Balance 6,673,405 8,585,872
Issued 1,379,739  
Cancelled (616,726) (141,084)
Exercised (12,177) (1,771,383)
Ending Balance 7,424,241 6,673,405