pre_text: Research and Development Research and development expenses increased $124.3 million, or 53.9%, for the year ended December 31, 2019 compared to the same period in 2018, due to an increase of $114.4 million in employee-related costs ($45.1 million of which related to stock-based compensation and related payroll taxes), a $7.4 million increase in computer hardware and software costs, and a $2.5 million increase in professional services fees, all as a result of growth in our research and development employee base and expanded development programs. Research and development expenses increased $94.7 million, or 69.6%, for the year ended December 31, 2018 compared to the same period in 2017, due to an increase of $89.6 million in employee-related costs, an increase of $3.1 million in computer hardware and software costs, and a $2.0 million increase in professional services fees, all as a result of growth in our research and development employee base and expanded development programs.
table: Years ended December 31, 2019 vs 2018 2018 vs 2017
table: 2019 2018 2017 % Change % Change
table: (in thousands, except percentages)
table: Research and development $ 355,015 $ 230,674 $ 135,997 53.9 % 69.6 %
table: Percentage of total revenues 22.5 % 21.5 % 20.2 %
question: Analyse this data from a financial earnings document. What is the average research and development expenses for 2017 and 2018?