Year	Percent
1986	25.4718
1987	21.9947
1988	19.2955
1989	15.8486
1990	13.3144
1991	11.7329
1992	10.7593
1993	14.7454
1994	16.8783
1995	17.1076
1996	20.0235
1997	17.9735
1998	10.741
1999	10.9996
2000	11.759
2001	11.9951
2002	12.0862
2003	16.7132
2004	15.9012
2005	19.157
2006	18.4989
2007	20.3144
2008	20.296
2009	21.6805
2010	24.0219
2011	31.6936
2012	39.2661
2013	39.5835
2014	35.3955
2015	34.4962
2016	28.7882
2017	25.5383