Table:
|  |  | Years Ended March 31, |  |
| --- | --- | --- | --- |
|  | 2019 | 2018 | 2017 |
| Amortization of intangible assets | $12,594 | $7,518 | $4,352 |
| Acquisition-related costs | 1,696 | 1,412 | 1,462 |
| Total | $14,290 | $8,930 | $5,814 |
Paragraphs:
Amortization of Intangibles and Acquisition-Related Costs
Amortization of intangibles included in operating expense and acquisition-related costs during fiscal years 2019 , 2018 and 2017 were as follows (in thousands):
Amortization of intangible assets consists of amortization of acquired intangible assets, including customer relationships and trademarks and trade names. Acquisition-related costs include legal expense, due diligence costs, and other professional costs incurred for business acquisitions.
The increase in amortization of intangible assets from fiscal year 2018 to 2019 was primarily due to the Blue Microphones Acquisition and the ASTRO Acquisition. The increase in amortization of intangible assets from fiscal year 2018 to 2017 was primarily driven by the ASTRO Acquisition.
Question:
What caused the increase in amortization of intangible assets in 2019?