pre_text: Product Licensing Segment (1) Excludes operating expenses which are not allocated on a segment basis. Product Licensing revenue for the year ended December 31, 2019 was $198.1 million as compared to $219.7 million for the year ended December 31, 2018, a decrease of $21.6 million. The decrease in revenue was primarily due to the timing and duration of minimum guarantee contracts up for renewal and executed, decreased NRE services revenue, as well as a decrease in per-unit royalty revenue in 2019 as compared to 2018.
table: Years Ended December 31,
table: 2019 2018 2017
table: (in thousands)
table: Revenue:
table: Royalty and license fees $198,124 $219,708 $167,923
table: Total revenue 198,124 219,708 167,923
table: Operating expenses:
table: Cost of revenues 8,460 13,291 6,308
table: Research, development and other related costs 83,613 78,892 75,809
table: Litigation 1,656 — 288
table: Amortization 88,075 88,544 90,340
table: Total operating expenses (1) 181,804 180,727 172,745
table: Total operating income (loss) $16,320 $38,981 $(4,822)
question: Analyse this data from a financial earnings document. What is the average total operating expense from 2017 to 2019?