Year	Percent
1999	16.9
2001	19.3
2002	15.1
2003	11.4
2004	7.9
2005	4.4
2006	3.2
2007	2.8
2008	1.4
2009	1.9
2010	1.9
2011	2.2
2012	1.6
2013	2.2
2014	2.3
2015	1.9
2016	1.8