Year	Number
1980	4949
1981	5390
1982	5973
1983	6450
1984	7057
1985	7725
1986	8069
1987	18640
1988	12351
1989	13294
1990	14466
1991	12457
1992	13321
1993	13894
1994	15874
1995	18632
1996	20442
1997	20487
1998	20918
1999	22970
2000	22961
2001	21391
2002	21019
2003	21744
2004	20837
2005	26582
2006	24010
2007	22950
2008	21848
2009	20107
2010	20850
2011	21142
2012	20167
2013	19688
2014	19086
2015	20661
2016	20119
2017	20179