Year ended December 31,
Year ended December 31,
(in thousands, except percentages)
2019
2018
$ Change
% Change
2018
2017
$ Change
% Change
Cost of revenues
Subscriptions
$160,320
$109,454
$50,866
46%
$109,454
$89,193
$20,261
23%
Other
70,723
47,675
23,048
48%
47,675
32,078
15,597
49%
Total cost of revenues
$231,043
$157,129
$73,914
47%
$157,129
$121,271
$35,858
30%
Percentage of revenues
Subscriptions
18%
16%
16%
18%
Other
8%
7%
7%
6%
Gross margins
Subscriptions
80%
82%
82%
81%
Other
17%
22%
22%
16%
Total gross margin %
74%
77%
77%
76%

text: Cost of Revenues and Gross Margin
text: 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.
text: 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.
text: 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.

Questions:
question: What are the respective drivers of the company's increased cost of revenue in 2019?
answer: third-party costs to support our solution offerings
infrastructure support costs
headcount and personnel and contractor related costs
question: What caused the increased in headcount and other expense?
answer: 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
question: What are the factors influencing the cost of revenues and gross margins in 2019?
answer: increase in services personnel costs
cost of product sales
overhead costs
question: What is the average cost of subscription between 2017 to 2019?
answer: 119655.67
derivation: (89,193 + 109,454 + 160,320)/3 
scale: thousand
question: What is the value of the subscription costs as a percentage of the total cost of revenue in 2019?
answer: 69.39
derivation: 160,320/231,043 
scale: percent
question: What is the average total cost of revenue between 2017 to 2019?
answer: 169814.33
derivation: (121,271 + 157,129 + 231,043)/3 
scale: thousand