Table:
|  |  | As of December 31, 2019 |  |  |
| --- | --- | --- | --- | --- |
|  | Amortized | Unrealized | Unrealized | Fair |
|  | Cost | Gains | Losses | Value |
| Foreign debt . | $387,775 | $551 | $506 | $387,820 |
| Foreign government obligations | 21,991 | 20 | — | 22,011 |
| U.S. debt | 65,970 | 176 | 12 | 66,134 |
| Time deposits | 335,541 | — | — | 335,541 |
| Total . | $811,277 | $747 | $518 | $811,506 |
Paragraphs:
During the year ended December 31, 2019, we sold marketable securities for proceeds of $52.0 million and realized no gain or loss on such sales. During the years ended December 31, 2018 and 2017, we sold marketable securities for proceeds of $10.8 million and $118.3 million, respectively, and realized gains of less than $0.1 million on such sales in each respective period. See Note 11. “Fair Value Measurements” to our consolidated financial statements for information about the fair value of our marketable securities.
The following tables summarize the unrealized gains and losses related to our available-for-sale marketable securities, by major security type, as of December 31, 2019 and 2018 (in thousands):
As of December 31, 2019, we had no investments in a loss position for a period of time greater than 12 months. As of December 31, 2018, we identified 15 investments totaling $207.2 million that had been in a loss position for a period of time greater than 12 months with unrealized losses of $1.8 million. The unrealized losses were primarily due to increases in interest rates relative to rates at the time of purchase. Based on the underlying credit quality of the investments, we generally hold such securities until we recover our cost basis. Therefore, we did not consider these securities to be other-than-temporarily impaired.
Question:
What were the reasons for the unrealized losses as at 31 December 2018?
Answer: The unrealized losses were primarily due to increases in interest rates relative to rates at the time of purchase.