pre_text: Cost of Revenues and Gross Margin Subscription cost of revenues and gross margin. Cost of subscriptions revenues increased by $50.9 million, or 46%, during fiscal year 2019 as compared to fiscal year 2018. Primary drivers of the increase were increases in third-party costs to support our solution offerings of $21.5 million, infrastructure support costs of $19.8 million including amortization expense from acquired intangible assets, and headcount and personnel and contractor related costs of $9.6 million including share-based compensation expense. These factors resulted in a decrease in gross margin. The increase in headcount and other expense categories described herein was driven primarily by investments in our infrastructure and capacity to improve the availability of our subscription offerings, while also supporting the growth in new customers and increased usage of our subscriptions by our existing customer base. We expect subscription gross margin to be within a relatively similar range in the future. Other cost of revenues and gross margin. Cost of other revenues increased by $23.0 million, or 48%, during fiscal year 2019 as compared to fiscal year 2018. This was primarily due to the increase in services personnel costs of $11.1 million including share-based compensation expense, cost of product sales of $10.6 million, and overhead costs of $1.3 million. Other revenues gross margin fluctuates based on timing of completion of professional services projects and discounting on phones.
table: Year ended December 31, Year ended December 31,
table: (in thousands, except percentages) 2019 2018 $ Change % Change 2018 2017 $ Change % Change
table: Cost of revenues
table: Subscriptions $160,320 $109,454 $50,866 46% $109,454 $89,193 $20,261 23%
table: Other 70,723 47,675 23,048 48% 47,675 32,078 15,597 49%
table: Total cost of revenues $231,043 $157,129 $73,914 47% $157,129 $121,271 $35,858 30%
table: Percentage of revenues
table: Subscriptions 18% 16% 16% 18%
table: Other 8% 7% 7% 6%
table: Gross margins
table: Subscriptions 80% 82% 82% 81%
table: Other 17% 22% 22% 16%
table: Total gross margin % 74% 77% 77% 76%
question: Analyse this data from a financial earnings document. What is the average total cost of revenue between 2017 to 2019?