Year	Number
1972	2646
1973	3121
1974	2944
1975	4008
1976	4161
1977	6375
1978	6346
1979	5736
1980	5590
1981	11280
1982	13741
1983	15831
1984	15699
1985	15996
1986	12634
1987	11467
1988	10990
1989	11141
1990	13905
1991	13659
1992	16311
1993	12307
2001	19612
2002	19170
2005	21511
2006	20301
2007	22712
2008	22551
2009	21897
2010	22557
2011	21284
2012	21363
2013	21329
2014	20704
2015	22437
2018	25412