Stock option plan (Details 4) (USD $)
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12 Months Ended | ||
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Dec. 31, 2013
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Dec. 31, 2012
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Dec. 31, 2011
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Share-based compensation expense recorded in the statement of operations | |||
Share-based compensation expense | $ 8,427,188 | $ 2,288,392 | $ 2,816,637 |
Unrecognized compensation cost | 21,600,000 | ||
Weighted average remaining service period for recognition of unrecognized compensation cost | 2 years 5 months 26 days | ||
Research and development
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Share-based compensation expense recorded in the statement of operations | |||
Share-based compensation expense | 2,039,880 | 804,576 | 916,495 |
General and administrative
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Share-based compensation expense recorded in the statement of operations | |||
Share-based compensation expense | $ 6,387,308 | $ 1,483,816 | $ 1,900,142 |