Year	Number
1971	30355
1972	29795
1973	28745
1974	28129
1975	22072
1976	21195
1977	20259
1978	19618
1979	19114
1980	18720
1981	18076
1982	17739
1983	17704
1984	17265
1985	17171
1986	16538
1987	17963
1988	18231
1990	19180
1991	19811
1992	21365
1993	22345
1994	22576
1995	22679
1996	21097
1997	23313
1998	22286
1999	20017
2000	16178
2001	15974
2002	17378
2003	16598
2004	15819
2005	14427
2007	13733
2008	13873
2009	14186
2010	13663
2011	13271
2013	12948
2014	13061
2015	13445
2016	13196
2017	13464
2018	13195
2021	11817