Year	Number
1971	7398
1972	7506
1973	7468
1974	7488
1975	7935
1976	8704
1977	8870
1978	9122
1979	9451
1980	55301
1981	94664
1982	100198
1983	107314
1984	108566
1985	114762
1986	122285
1987	129644
1988	135564
1989	144636
1990	145390
1991	146401
1992	100319
1999	77425
2000	97627
2002	119777
2003	140433
2004	163076
2005	178582
2006	197671
2007	223169
2008	241143
2009	292129
2011	426979
2012	476281
2013	501504
2014	499126
2015	467709
2016	478695
2017	531377
2018	569711