Year Number 2004-01-01 10 2005-01-01 10 2006-01-01 9 2007-01-01 12 2008-01-01 12 2009-01-01 12 2010-01-01 13 2011-01-01 15 2012-01-01 17 2013-01-01 17 2014-01-01 16 2015-01-01 16 2016-01-01 17 2017-01-01 16