pre_text: Stock-Based Compensation A summary of our stock-based compensation expense is as follows (in thousands): (1) Amount for the year ended December 31, 2018 includes $4.1 million of accelerated stock-based compensation expense. In March 2018, as
  a result of a suspension of the 2014 Purchase Plan due to our non-timely filing status, all unrecognized stock-based compensation expense
  related to ESPP under the 2014 Purchase Plan was accelerated and recognized within the consolidated statement of operations. As of December 31, 2019, we had $29.5 million of unrecognized stock-based compensation expense related to
  unvested stock-based awards, including ESPP under our Amended 2014 Purchase Plan, which will be recognized
  over a weighted-average period of 2.6 years.
table: Years Ended December 31,
table: 2019 2018 2017
table: Stock-based compensation by type of award:
table: Stock options $648 $1,353 $2,705
table: Stock awards 14,882 10,445 11,421
table: Employee stock purchase rights(1) 999 5,240 3,077
table: Total $16,529 $17,038 $17,203
table: Stock-based compensation by category of expense:
table: Cost of revenue $1,500 $1,602 $1,362
table: Sales and marketing 5,765 5,667 6,075
table: Research and development 6,039 6,631 6,343
table: General and administrative 3,225 3,138 3,423
table: Total $16,529 $17,038 $17,203
question: Analyse this data from a financial earnings document. What is the total stock based compensation amount between 2017 to 2019?