Year	Percent
1987	9.17
1988	16.15
1989	15.44
1990	15.43
1991	15.2
1992	14.74
1993	14.78
1994	14.78
1995	14
1996	14.4
1997	14.34
1998	13.99
1999	14.34
2000	13.31
2001	52.83
2002	54.19
2003	55.05
2004	55.74
2005	56.39
2006	58.16
2007	59.4
2008	60.72
2009	53.49
2010	53.6
2011	53.78
2012	53.88
2013	55.18
2014	59.09
2015	60.05
2016	60.16
2017	60.3