|
Income taxes (Details 2) (USD $)
|
Dec. 31, 2013
|
Dec. 31, 2012
|
|---|---|---|
| Deferred Tax Assets [Line Items] | ||
| Net operating loss carryforwards | $ 31,541,018 | $ 28,564,716 |
| Stock based compensation expense | 9,923,714 | 9,173,701 |
| Tax credit carryforwards and other | 1,241,115 | 1,033,887 |
| Gross deferred tax asset | 42,705,847 | 38,772,304 |
| Valuation allowance | (42,705,847) | (38,772,304) |
| Net deferred tax assets | $ 0 | $ 0 |