Year	% of revenue
2010	17.08715724434436
2012	19.77082684363993
2013	19.39667196509084
2014	19.790990442402432
2015	21.1985871397845
2016	20.660451819573407
2017	21.983561879360145
2018	23.538275906239832
2019	23.078694421340863
2020	24.219367141888675