Year	Number
1971	4200
1972	4576
1973	4124
1974	5409
1975	6002
1976	6480
1977	7073
1978	7493
1979	8014
1980	8443
1981	10114
1982	9889
1983	10946
1984	11808
1985	12594
1986	12902
1987	12229
1988	12937
1989	12674
1990	15171
1991	7434
1992	8064
1993	9332
2001	8542
2002	9293
2003	10127
2004	11516
2005	11870
2006	11912
2007	12630
2009	13796
2010	15465
2011	18930
2012	17384
2013	26149
2014	37026
2015	48297
2016	50885
2017	67110
2018	68831