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Share-based compensation 2 (Details) (USD $)
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6 Months Ended |
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Jun. 30, 2012
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| Share-Based Compensation [Abstract] | |
| Dividend Yield | 0.00% |
| Expected volatility | 50.00% |
| Expected term of options | 4.5 |
| Risk free interest rate minimum | 0.68% |
| Risk free interest rate maximum | 0.75% |
| Weighted average grant date fair value minimum | $ 2.56 |
| Weighted average grant date fair value maximum | $ 3.12 |