Year Percent 2011-01-01 17.437100000000000 2012-01-01 17.437100000000000 2013-01-01 17.437100000000000 2014-01-01 18.237000000000002 2015-01-01 18.237000000000002 2016-01-01 18.237000000000002 2017-01-01 21.338100000000000