Year	Number of
1983	12660
1984	12380
1985	12290
1986	12400
1987	12540
1988	12760
1989	12910
1990	13000
1991	12820
1992	12680
1993	12490
1994	12590
1995	13000
1996	13320
1997	13900
1998	14620
1999	15360
2000	15910
2001	16310
2002	16510
2003	16610
2004	16690
2005	16890
2006	17300
2007	17720
2008	18140
2009	18400
2010	18550
2011	18440
2012	18250
2013	17960
2014	17760
2015	17690