| Year | Value | | 2021 | 18,620 | | 2020 | 18,611 | | 2019 | 18,538 | | 2018 | 18,536 | | 2017 | 18,513 | | 2016 | 18,429 | | 2015 | 18,510 | | 2014 | 18,942 | | 2013 | 18,959 | | 2012 | 19,617 | | 2011 | 19,725 | | 2010 | 19,702 | | 2009 | 19,764 | | 2008 | 19,627 | | 2007 | 19,419 | | 2006 | 19,429 | | 2005 | 19,599 | | 2004 | 19,617 | | 2003 | 19,900 | | 2002 | 20,223 | | 2001 | 20,134 | | 2000 | 22,560 | | 1999 | 22,891 | | 1998 | 23,210 | | 1997 | 23,328 | | 1996 | 23,420 | | 1995 | 23,986 |
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