Year Percent 2004-01-01 19.036600000000000 2005-01-01 24.118000000000002 2006-01-01 31.010200000000000 2007-01-01 31.415900000000000 2008-01-01 35.518800000000000 2009-01-01 38.678500000000000 2010-01-01 34.747800000000000 2011-01-01 32.345500000000000 2012-01-01 29.476700000000000 2013-01-01 29.458200000000000 2014-01-01 31.063800000000000 2015-01-01 30.739400000000000 2016-01-01 34.402100000000000 2017-01-01 36.028900000000000