Year	Number
1971	3408
1972	3745
1973	4072
1974	4716
1975	5493
1976	6571
1977	7995
1978	9660
1979	11957
1980	17427
1981	20248
1982	22834
1983	25700
1984	27924
1985	30840
1986	33148
1987	35129
1988	37412
1989	37370
1990	35758
1991	36177
1992	38039
1993	41071
1994	43861
1995	46917
1996	49221
1997	50095
1998	54776
1999	60029
2000	63735
2001	74742
2002	76837
2003	81278
2004	85588
2005	89540
2006	95772
2007	98730
2008	95497
2009	104554
2010	108499
2011	122595
2012	149633
2013	169126
2014	176915
2015	186502
2016	198457
2017	201363
2018	235653