Year	Number
1970	10421
1971	11362
1972	12127
1973	12479
1974	12906
1975	13687
1976	15077
1977	15204
1978	15571
1979	15996
1980	16532
1981	16805
1982	17698
1983	18854
1984	18565
1985	18889
1986	18717
1989	18687
1991	24142
1992	25115
1993	26199
1994	26700
1995	29265
1996	28274
1998	30956
1999	32578
2000	33347
2001	34837
2002	36631
2003	37743
2004	39553
2005	40890
2006	42598
2007	42943
2008	43345
2009	44430
2010	44806
2011	45626
2012	46432
2013	44877
2014	43387
2015	41735
2016	40731
2017	39992
2018	38822