Year	Percent
1987	17.6
1994	17.1
1998	15.7
1999	21.8
2000	28.2
2003	14.5
2004	15
2005	12.1
2006	8.1
2007	8.5
2008	7.5
2009	7.2
2010	5.6
2011	4.7
2012	4.5
2013	3.2
2014	2.6
2015	3.4
2016	3.6