Year Percent 2003-01-01 56.050 2004-01-01 56.400 2005-01-01 56.750 2006-01-01 57.000 2007-01-01 57.525 2008-01-01 57.850 2009-01-01 58.375 2010-01-01 58.450 2011-01-01 58.350 2012-01-01 58.625 2013-01-01 58.875 2014-01-01 58.725 2015-01-01 58.650 2016-01-01 58.525 2017-01-01 58.225