Year	Number
1980	9106
1981	10556
1982	9772
1983	10415
1984	12396
1985	12894
1986	12694
1987	11837
1988	15262
1989	15181
1990	13948
1991	12253
1992	12573
1993	13068
1994	14391
1995	14938
1996	17895
1997	18519
1998	18189
1999	20502
2000	22080
2001	17314
2002	17068
2003	18072
2004	17719
2005	18777
2006	19949
2007	21101
2008	20040
2009	18663
2010	20449
2011	21337
2012	21741
2013	21449
2014	21348
2015	22589
2016	23652
2017	25853