Documents | Strength | Begin | End |
| 13.17 | 2008 | 2011 |
| 9.69 | 2008 | 2011 |
| 8.67 | 2008 | 2010 |
| 9 | 2010 | 2013 |
| 8.84 | 2011 | 2014 |
| 14.46 | 2012 | 2015 |
| 11.02 | 2013 | 2016 |
| 8.53 | 2014 | 2017 |
| 10.97 | 2016 | 2019 |
| 8.72 | 2018 | 2021 |