pre_text: Research and Development Research and development expenses increased $24.2 million, or 31%, in 2019 as compared to 2018. The increase was principally due to the 2018 Reallocation of headcount from sales and marketing to research and development, as well as investments to maintain and improve the functionality of our products. As a result, we incurred increased employee-related costs of $16.3 million and increased overhead costs of $3.4 million. Research and development expenses increased $15.0 million, or 24%, in 2018 as compared to 2017. The increase was principally due to the 2018 Reallocation of headcount from sales and marketing to research and development, as well as investments to maintain and improve the functionality of our products. As a result, we incurred increased employee-related costs of $12.1 million.
table: Year Ended December 31,
table: 2019 2018 2017
table: (dollars in thousands)
table: Research and development $101,151 $76,981 $61,975
table: Percent of revenue 17.5% 14.3% 12.9%
question: Analyse this data from a financial earnings document. What was the average research and development from 2017-2019?