Year	Number of
1990	16.76
1991	18.3
1992	20
1993	21.66
1994	23.68
1995	26.09
1996	29.04
1997	32.48
1998	36.19
1999	40.14
2000	44.42
2001	47.68
2002	51.68
2003	57.69
2004	66.82
2005	80.29
2006	91.37
2007	107.4
2008	127.39
2009	148.89
2010	170.45
2011	201.04
2012	231.55
2013	263
2014	297.58
2015	337.9
2016	388.06