Year Percent 2005-01-01 18.675 2006-01-01 17.575 2007-01-01 15.825 2008-01-01 15.750 2009-01-01 18.975 2010-01-01 20.200 2011-01-01 20.875 2012-01-01 22.950 2013-01-01 23.750 2014-01-01 23.225 2015-01-01 21.650 2016-01-01 20.300 2017-01-01 18.150