Year Percent 2005-01-01 51.875 2006-01-01 52.900 2007-01-01 54.025 2008-01-01 54.775 2009-01-01 54.800 2010-01-01 55.225 2011-01-01 56.600 2012-01-01 56.850 2013-01-01 57.175 2014-01-01 57.400 2015-01-01 57.400 2016-01-01 58.500 2017-01-01 58.900