Year	Percent
1986	25.09
1987	24.61
1988	24.4
1989	25.2
1990	27.87
1991	26.55
1992	22.54
1993	21.36
1994	19.34
1995	16.72
1996	14.57
1997	13.53
1998	13.05
1999	11.55
2000	10.48
2001	10.35
2002	11.99
2003	15.02
2004	17.58
2005	17.58
2006	19.4
2007	20.28
2008	20.65
2012	21.71
2013	20.21
2014	20.43
2015	20.9
2016	22.09
2017	23.14