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Income taxes - Income Tax Expense (Detail) (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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| Income Tax Disclosure [Abstract] | ||
| Current | $ 18,000 | $ 32,921 |
| Deferred | (13,229,355) | (6,289,888) |
| Valuation allowance | 13,229,355 | 6,289,888 |
| Provision for income taxes | $ 18,000 | $ 32,921 |