Year	Number of
1990	20.71
1991	21.9
1992	23.05
1993	24.04
1994	25.24
1995	26.66
1996	27.95
1997	29.44
1998	30.63
1999	31.92
2000	33.05
2001	33.88
2002	34.92
2003	36.21
2004	38.87
2005	44.4
2006	49.46
2007	55.59
2008	64.32
2009	74.94
2010	85.06
2011	97.14
2012	107.85
2013	117.71
2014	127.72
2015	138.21
2016	150.22