Year	Number
1972	3388
1973	3522
1974	3877
1975	4181
1976	4136
1977	4191
1978	4417
1980	4879
1981	4306
1982	4827
1983	4982
1984	4989
1985	5635
1986	6239
1987	6423
1988	6684
1990	7469
1991	7959
1992	8825
1993	9550
1999	11847
2000	12530
2001	12738
2002	12743
2003	12662
2004	12239
2005	12840
2006	13774
2007	14862
2008	15774
2009	16075
2010	15889
2011	15449
2012	14565
2013	13910
2014	13437
2015	13040
2016	12532
2017	12067
2018	11655