Year	Number of
1990	223.1
1991	229.46
1992	236.11
1993	242.92
1994	251.02
1995	258.98
1996	264.61
1997	270.77
1998	277.37
1999	285.13
2000	292.48
2001	297.45
2002	302.91
2003	309.41
2004	316.53
2005	322.83
2006	343.43
2007	355.49
2008	377.4
2009	401.96
2010	425.04
2011	456.88
2012	480.61
2013	505.67
2014	532.39
2015	560.98
2016	593.06