| Current (4) |
| Chairman | 2018 |
| Board of Directors | 2018 |
| Board of Directors | 2015 |
| Board of Directors | 2011 |
| Former (15) |
| Board of Directors | 2011 – 2015 |
| Board of Directors | 2016 – 2018 |
| Board of Directors | 1971 – 1991 |
| Board of Directors | 1971 – 1999 |
| Chairman | 1971 – 2018 |
| Board of Directors | 1999 – 2009 |
| Board of Directors | 1999 – 2008 |
| Board of Directors | 2009 – 2015 |
| Board of Directors | 1999 – 2008 |
| Board of Directors | 1999 – 2001 |
| Board of Directors | 2015 – 2016 |
| Board of Directors | 2009 – 2011 |
| Board of Directors | 1971 – 1999 |
| Board of Directors | 1971 – 1999 |
| Board of Directors | 1971 – 1992 |