Table:
|  |  | Years Ended December 31, |  |
| --- | --- | --- | --- |
|  | 2019 | 2018 | 2017 |
|  |  | (in thousands) |  |
| Revenue: |  |  |  |
| Royalty and license fees | $81,943 | $186,425 | $205,809 |
| Total revenue | 81,943 | 186,425 | 205,809 |
| Operating expenses: |  |  |  |
| Research, development and other related costs | 28,732 | 27,514 | 30,039 |
| Litigation | 3,471 | 26,099 | 36,209 |
| Amortization | 11,871 | 19,906 | 21,590 |
| Total operating expenses (1) | 44,074 | 73,519 | 87,838 |
| Total operating income | $37,869 | $112,906 | $117,971 |
Paragraphs:
Semiconductor and IP Licensing Segment
(1) Excludes operating expenses which are not allocated on a segment basis.
Semiconductor and IP Licensing segment revenue for the year ended December 31, 2019 was $81.9 million as compared to $186.4 million for the year ended December 31, 2018, a decrease of $104.5 million. The decrease in revenue was due principally to revenue recorded in 2018 related to the Samsung settlement and license agreement executed in December 2018, partially offset by a one-time payment from a new license agreement signed in December 2019.
Question:
What was the primary cause of the decrease in revenue in 2019 compared to 2018?
Answer: revenue recorded in 2018 related to the Samsung settlement and license agreement executed in December 2018, partially offset by a one-time payment from a new license agreement signed in December 2019