| Year | |
|---|---|
| 1989 | 1,304.0 |
| 1990 | 1,304.0 |
| 1991 | 1,304.0 |
| 1992 | 1,304.0 |
| 1993 | 1,304.0 |
| 1994 | 1,304.0 |
| 1995 | 1,304.0 |
| 1996 | 1,277.0 |
| 1997 | 1,277.0 |
| 1998 | 1,277.0 |
| 1999 | 1,277.0 |
| 2000 | 1,277.0 |
| 2001 | 1,442.0 |
| 2002 | 1,417.7 |
| 2003 | 1,417.7 |
| 2004 | 1,417.7 |
| 2005 | 1,411.4 |
| 2006 | 1,411.4 |
| 2007 | 1,411.4 |
| 2008 | 1,411.4 |
| 2009 | 1,411.4 |
| 2010 | 1,389.1 |
| 2011 | 1,389.1 |
| 2012 | 1,389.1 |
| 2013 | 1,620.0 |
| 2014 | 1,620.0 |
| 2015 | 1,620.0 |
| 2016 | 1,625.0 |
| 2017 | 1,625.0 |