Year Percent 2005-01-01 56.200 2006-01-01 57.075 2007-01-01 58.000 2008-01-01 58.325 2009-01-01 57.025 2010-01-01 56.675 2011-01-01 56.825 2012-01-01 56.425 2013-01-01 56.075 2014-01-01 56.300 2015-01-01 56.825 2016-01-01 57.700 2017-01-01 58.400