Year	Percent
1999-01-01	80.550
2000-01-01	80.075
2001-01-01	79.450
2002-01-01	79.575
2003-01-01	79.875
2004-01-01	77.350
2005-01-01	78.025
2006-01-01	78.875
2007-01-01	79.950
2008-01-01	80.000
2009-01-01	79.975
2010-01-01	80.050
2011-01-01	79.900
2012-01-01	80.250
2013-01-01	80.400
2014-01-01	80.000
2015-01-01	80.100
2016-01-01	80.675
2017-01-01	81.025