Year	Number
1971	19746
1972	24595
1973	28320
1974	34125
1975	44306
1976	59162
1977	74567
1978	88409
1979	105770
1980	119801
1981	125122
1982	122925
1983	112861
1984	95941
1985	85745
1986	91609
1987	92289
1988	108557
1989	103835
1990	120572
1991	117153
1992	120289
1994	126335
1995	145717
1996	161672
1997	169178
1998	186410
1999	216484
2000	243590
2001	269776
2002	309551
2003	334864
2004	355547
2005	377156
2006	402224
2007	377118
2008	409145
2009	424500
2010	460032
2011	518288
2012	524750
2013	534174
2014	539695
2015	578929
2016	598939
2017	685737
2018	711617