Table:
|  |  | Years Ended September 30, |  |
| --- | --- | --- | --- |
|  | 2019 | 2018 | 2017 |
| Cost of sales | $  1,766 | $  1,096 | $  338 |
| Selling, general and administrative | 13,722 | 6,419 | 4,674 |
|  | $15,488 | $7,515 | $5,012 |
Paragraphs:
We recorded non-cash compensation expense related to stock-based awards as follows (in thousands):
As of September 30, 2019, there was $39.7 million of unrecognized compensation expense related to unvested RSUs. Based upon the expected forfeitures and the expected vesting of performance-based RSUs, the aggregate fair value of RSUs expected to ultimately vest is $40.0 million, which is expected to be recognized over a weighted-average period of 1.7 years and includes the RSUs that vested on October 1, 2019.
We estimate forfeitures at the time of grant and revise those estimates in subsequent periods on a cumulative basis in the period the estimated forfeiture rate changes for all stock-based awards when significant events occur. We consider our historical experience with employee turnover as the basis to arrive at our estimated forfeiture rate. The forfeiture rate was estimated to be 12.5% per year as of September 30, 2019. To the extent the actual forfeiture rate is different from what we have estimated, compensation expense related to these awards will be different from our expectations.
Question:
For which years is the amount of non-cash compensation expense related to stock-based awards recorded?
Answer: 2019, 2018, 2017