Year	Number
1971	3649
1972	4476
1973	5443
1974	6301
1975	7139
1976	9416
1977	9716
1978	10915
1979	12445
1980	13913
1981	15461
1982	16696
1983	18346
1984	19037
1985	20398
1986	21874
1987	21588
1988	23818
1989	25735
1990	27758
1991	29154
1992	30277
1993	34231
1994	35518
1995	36964
1996	37924
1998	41959
1999	43662
2000	46653
2001	46338
2002	48490
2003	51331
2004	53460
2005	55186
2006	58203
2007	60451
2008	65480
2009	65952
2010	68322
2011	72149
2012	76323
2013	78436
2014	87878
2015	94902
2016	97430
2017	102367
2018	106817