|
Stock options and restricted common stock - Assumptions used to value the most recent option grants (Details)
|
12 Months Ended |
|
Dec. 31, 2013
|
Dec. 31, 2012
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
| Estimated expected term |
|
6 years |
| Risk free interest Rate, minimum |
1.70% |
|
| Risk-free interest rate |
|
0.98% |
| Risk free interest Rate, maximum |
2.22% |
|
| Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Minimum |
64.00% |
|
| Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Maximum |
68.00% |
|
| Expected volatility assumption |
|
66.00% |
| Dividend yield assumption |
0.00% |
0.00% |
|
Minimum [Member]
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
| Estimated expected term |
6 years |
|
| Forfeiture rate |
0.00% |
0.00% |
|
Maximum [Member]
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
| Estimated expected term |
8 years |
|
| Forfeiture rate |
7.00% |
7.00% |