Year	Number
1980	4308
1981	4590
1982	3995
1983	3729
1984	4057
1985	8495
1986	10629
1987	11047
1988	15606
1989	17920
1990	19110
1991	18819
1992	18979
1993	18388
1994	19256
1995	18223
1996	13938
1997	14825
1998	12253
1999	15288
2000	18571
2001	16306
2002	14334
2003	14785
2004	15071
2005	14382
2006	17104
2007	20005
2008	19852
2009	18717
2010	19452
2011	18349
2012	16662
2013	16981
2014	19668
2015	18509
2016	18694
2017	20383