Year	Percent
2001	16.34
2002	16.28
2003	16.96
2004	17.41
2005	18.01
2006	18.44
2007	18.92
2008	18.92
2009	18.64
2010	18.72
2011	18.96
2012	19.38
2013	19.82
2014	19.68
2015	20.56
2016	20.98
2017	20.34