Year Percent 2003-01-01 55.600 2004-01-01 55.500 2005-01-01 56.500 2006-01-01 56.300 2007-01-01 57.400 2008-01-01 56.600 2009-01-01 58.175 2010-01-01 58.300 2011-01-01 57.675 2012-01-01 59.000 2013-01-01 59.075 2014-01-01 59.825 2015-01-01 60.450 2016-01-01 59.725 2017-01-01 59.925