Year	Number
1981	14397
1982	14691
1983	15870
1984	16306
1985	15914
1986	17810
1987	18227
1988	19582
1989	18846
1990	20681
1991	21994
1992	22982
1993	27485
1994	37097
1995	42723
1996	43234
1997	43302
1998	51704
1999	65730
2000	84275
2001	90236
2002	94120
2003	92251
2004	78996
2005	85669
2006	103421
2007	123514
2008	130172
2009	141943
2010	189926
2011	198547
2012	190851
2013	202818
2014	223756
2015	274822
2016	296321
2017	266029