Year	Number
1980	13538
1981	7627
1982	6913
1983	8808
1984	3781
1985	6318
1986	6991
1987	6296
1988	7183
1989	8580
1990	9579
1991	10597
1992	11477
1993	12788
1994	14619
1995	14049
1996	12774
1997	13929
1998	15373
1999	16657
2000	23023
2001	21252
2002	18473
2003	18961
2004	20239
2005	22219
2006	24620
2007	28607
2008	27695
2009	22660
2010	25529
2011	29190
2012	29818
2013	27097
2014	28831
2015	29759
2016	30180
2017	30400