Year Percent 2005-01-01 56.575 2006-01-01 57.425 2007-01-01 58.250 2008-01-01 58.700 2009-01-01 57.525 2010-01-01 57.225 2011-01-01 57.250 2012-01-01 57.100 2013-01-01 56.950 2014-01-01 57.475 2015-01-01 58.075 2016-01-01 58.900 2017-01-01 59.725