Year	Number
1970	15317
1971	8815
1972	10006
1973	13792
1975	16476
1976	17795
1977	18955
1978	19512
1979	23368
1980	25292
1981	28107
1982	29608
1983	33421
1984	35444
1985	37343
1986	39478
1987	43368
1988	45951
1989	47212
1990	48209
1991	48505
1992	52598
1993	55984
1994	62399
1995	67173
1996	68132
1997	72170
1998	72235
1999	73620
2000	74313
2001	79266
2002	82256
2003	84273
2004	89864
2005	94496
2006	96073
2007	101738
2008	107322
2009	115805
2010	125823
2011	130831
2012	134543
2013	130476
2014	130836
2015	133434
2016	128780
2017	136497