Table:
|  |  | Years Ended December 31, |  |
| --- | --- | --- | --- |
|  | 2019 | 2018 | 2017 |
|  |  | (in thousands) |  |
| Cost of net revenue | $577 | $489 | $332 |
| Research and development | 16,545 | 17,953 | 16,190 |
| Selling, general and administrative | 14,938 | 13,279 | 11,016 |
| Restructuring expense | — | — | 5,130 |
|  | $32,060 | $31,721 | $32,668 |
Paragraphs:
Stock-Based Compensation
The Company recognizes stock-based compensation expense in the consolidated statements of operations, based on the department to which the related employee reports, as follows: The Company recognizes stock-based compensation expense in the consolidated statements of operations, based on the department to which the related employee reports, as follows:
The total unrecognized compensation cost related to performance-based restricted stock units as of December 31, 2019 was $3.6 million, and the weighted average period over which these equity awards are expected to vest is 1.6 years. The total unrecognized compensation cost related to unvested stock options as of December 31, 2019 was $2.0 million, and the weighted average period over which these equity awards are expected to vest is 2.30 years.
Question:
In which year was Restructuring expense 0 thousands?
Answer: Because locate and analyze Restructuring expense in row 7, the answers are: 2019, 2018.