Year	Number of
1954	17370
1955	17550
1956	17740
1957	17940
1958	18120
1959	18310
1960	18650
1961	19140
1962	19730
1963	20260
1964	20570
1965	20580
1966	20200
1967	19560
1968	18750
1969	17940
1970	17170
1971	16510
1972	15860
1973	15320
1974	14840
1975	14390
1976	14030
1977	13680
1978	13280
1979	12750
1980	12140
1981	11340
1982	10530
1983	9735
1984	9018
1985	8419
1986	7955
1987	7572
1988	7396
1989	7450
1990	7657
1991	7939
1992	8141
1993	8062
1994	7766
1995	7414
1996	7250
1997	7243
1998	7208
1999	7123
2000	6957
2001	6777
2002	6525
2003	6201
2004	5808
2005	5525
2006	5597
2007	5783
2008	6025
2009	6086
2010	6028
2011	5919
2012	5810
2013	5700
2014	5524
2015	5339