Year	Percent
1997-01-01	1.46
1998-01-01	4.00
1999-01-01	6.86
2000-01-01	10.09
2001-01-01	11.66
2002-01-01	14.86
2003-01-01	18.60
2004-01-01	19.70
2005-01-01	21.28
2006-01-01	19.82
2007-01-01	21.13
2008-01-01	22.20
2009-01-01	26.24
2010-01-01	27.30
2011-01-01	27.10
2012-01-01	28.42
2013-01-01	29.97
2014-01-01	32.03
2015-01-01	36.83
2016-01-01	41.30