Year Number of 1990 15336.75 1991 15994.6 1992 15842.29 1993 15547.4 1994 15710.59 1995 16306.61 1996 16113.02 1997 16499.62 1998 16734.46 1999 17614.56 2000 17330.3 2001 17306.17 2002 17351.84 2003 17405.16 2004 17728.23 2005 17822.7 2006 17971.75 2007 18156 2008 18108.48 2009 18015.28 2010 17894.4 2011 17799.8 2012 18022.05 2013 17859.17 2014 17261.52 2015 17090.33 2016 16983.55