Year	% of revenue
2010	18.53437170680675
2012	19.899790073203206
2013	19.461079948497833
2014	19.790990442402432
2015	20.999278504239363
2016	20.79066750650199
2017	21.84455613557035
2018	22.92235707019728
2019	22.622330622266603
2020	24.280369594719623
2021	24.836908904874537