Year	Percent
1998-01-01	83.700
1999-01-01	81.925
2000-01-01	81.575
2001-01-01	82.100
2002-01-01	82.500
2003-01-01	81.675
2004-01-01	81.400
2005-01-01	82.000
2006-01-01	82.550
2007-01-01	83.450
2008-01-01	83.850
2009-01-01	82.500
2010-01-01	82.150
2011-01-01	82.825
2012-01-01	82.975
2013-01-01	83.500
2014-01-01	83.825
2015-01-01	84.500
2016-01-01	85.725
2017-01-01	86.675