|
Share-based compensation 4 (Details) (USD $)
|
6 Months Ended |
|---|---|
|
Jun. 30, 2012
|
|
| Share-Based Compensation [Abstract] | |
| Number of Shares nonvested Start | 402,148 |
| Number of Shares Granted | 398,428 |
| Number of Shares Vested | (138,147) |
| Number of Shares Canceled or forfeited | (5,048) |
| Number of Shares nonvested End | 657,381 |
| Weighted Average Grant Date Fair Value Nonvested Start | $ 11.40 |
| Weighted Average Grant Date Fair Value Granted | $ 6.17 |
| Weighted Average Grant Date Fair Value Vested | $ 11.42 |
| Weighted Average Grant Date Fair Value Canceled or forfeited | $ 9.92 |
| Weighted Average Grant Date Fair Value Nonvested End | $ 8.24 |