Year	Number
1970	3784
1971	4460
1972	5039
1973	5426
1974	5780
1975	5666
1976	5701
1977	5882
1978	5952
1979	6202
1980	8138
1981	8610
1982	8924
1983	9184
1984	9491
1985	9681
1986	9873
1987	10068
1988	9796
1989	9968
1990	9754
1991	9996
1992	10521
1993	10979
1994	11440
1995	11817
1996	12239
1999	14380
2000	14404
2001	15181
2002	15613
2004	16109
2005	16392
2006	16317
2007	16847
2008	17337
2009	18750
2010	18501
2011	19463
2013	20001
2014	22946
2015	23777
2016	23777
2017	23777