Year	Number
1971	20495
1972	21578
1973	22433
1974	25307
1975	26512
1976	28056
1977	29472
1978	29832
1979	30015
1980	29734
1981	28136
1982	27731
1983	27649
1984	29496
1985	27147
1986	27604
1987	29765
1990	26835
1991	26861
1992	29559
1993	29863
1994	28532
1995	28435
1997	27970
1999	26614
2002	31713
2004	30857
2005	32089
2006	32709
2007	34217
2008	34399
2009	34274
2010	34406
2011	32973
2012	33351
2013	29939
2014	31681
2015	25766
2016	28384
2017	30740
2018	26884